While rare, HLH is also potentially life-threatening, so pediatric hematologist-oncologist Michelle Hermiston, MD, PhD, wants pediatricians to understand when and how to think about this hyperinflammatory syndrome. Her talk presents the etiologies, offers pearls on understanding the cytokine storm and delineates when to suspect HLH (think: unexplained, excessive immune response to illness). Hermiston describes keys to the workup, explains why knowing the trigger is essential to effective treatment and discusses which patients should receive a stem cell transplant.
So, um, I was asked, um, to speak today on, um, hemophagocytic lymphophysiocytosis. Um, these are my disclosures. I do sit on external advisory boards for Novartis, Soby Pharmaceuticals and Maton and except oops. Except for immapoliumab and refractory HLH, no drugs are approved for HLH in the United States. So, um, today what I would like to cover is to define HLH as a clinical syndrome that can be caused by multiple etiologies, to explain the pathophysiology of HLH and its common manifestations, to describe a systematic approach to the patient with suspected HLH and to review treatment options for hyperinflammatory conditions. Oops, there we go. I thought I would start here. Um, this is an email from my son a few years ago. He's, um, our family are big hockey fans and he said this is pretty cool. Blues hockey team is supporting this little girl who had a transplant for this disease called HLH hemophagal something something. Don't know if you know anything about HLH but it sounds really bad. Thought you'd enjoy the video. And indeed this is a very rare disease, um, so you know, hopefully a little bit or a lot about it and I'm able to share that with you today. Um, and, uh, it certainly can be a very bad disease. So, let's dig in, um, and try to, um, help us all develop a systematic approach to this entity. So what is HLH? If we break it down into its Latin roots, heme is blood, phagocytic is of a cell that eats, and lymphocytosis is expansion of lymphocytes. What we see, um, histologically are, um, Uh, swollen swollen macrophages who ingest um essentially cells, so white blood cells, there's some platelets in there and there's some red blood cells inside this cell. Um, it's important to understand that HLH is not a single disease entity. There is not one test we can send that says, oh, this is HLH. It's actually a syndrome, which is a clinical manifestation of many different conditions. It's characterized by uncontrolled and massive systemic inflammation involving lymphocytes and macrophages, and can be thought of as hyperinflammation that becomes self-damaging and often life-threatening. This is a figure from a review that we wrote as part of the North American Consortium for Histeocytosis that um shows all the different diseases that can fall under um the umbrella of HLH syndrome, disease, and mimics. And so um the um understanding and the approach these patients can be quite complex and generally takes a large team of individuals. I find it helpful to take a step back and to try to think about this very simplistically. What is our immune system designed to do? It's role is really to eliminate infected cells or malignant cells, and we know that patients without a functional immune system have increased infections and also increased risk for malignancy, particularly lymphoid malignancies. So in a normal individual, you have a trigger, infection malignancy. Once in a while it's a self-antigen if the immune system is confused and has reactivity. Um, to self and autoimmune disease, but any of these triggers can lead to activation of CD8 T cells. These T cells, when they are activated, um, start to proliferate, and they produce interferon gamma that leads to recruitment and activation of neutrophils, macro and macrophages, um, which are able to clear the virus. Seems to be in the timer. Um, the important part of this is that they will produce more cytokines from these infected monocytes, um, or um activated cells, and that leads to further activation of the T cells. Um, these T cells can recognize and, um, through cytolytic granule release, kill the infected, um, target. cell or the malignant target cell. Once the target is eliminated, this then leads to, um, no further stimulation for the T cells. Most of them will die and a few will go on to become memory T cells. And this protects us the next time we um encounter that same antigen. In individuals with HLH it's important to recognize that the immune response is appropriately initiated. The challenge is really in the ability to terminate that immune response, and so the process starts appropriately, get interferon gamma, macrophages get activated, they release their appropriate goodies, aisle 6. TNF and IL-18. Um, however, the T cells due to cytolytic defects are unable to stop this immune response and so you get this very, um, active and vicious circle with hypercytic anemia that leads to cell infiltration and destruction of tissues, um, uh, in a very ill patient. So in familial HLH, which is really I think taught us a lot about this defect, it's quite fascinating that the defects um in families um mapped to different steps in the cytolytic um pathways. So RAB 27, MOC 13, MOC 18 or cyto. Toxin or syntoxin 11 and all of these different proteins are important for movement of the cytolytic granules to the cell's surface. You can also have a um mutation in perference. You can't poke a hole into the target cell and kill it. And with this defect, you have this activated cell. That, sorry about that, um, is producing lots of cytokines but unable to kill the target cell. We know that there are at least 5 types of familial HLH which historically has been thought of as the genetic kind. Um, it's important to point out that FH FHL1 is still unknown despite complete sequencing and it's despite the fact that two family members in this um uh family um died of an HLH-like syndrome. So we still don't know all of Um, the genes, um, and pathways that are important for this disease. There's also a number of HLH associated immune deficiencies such as Sheriakagashi disease, Roselli syndrome, X-linked, um, lymphoroliferative disorder 1 and 2, and ITK deficiency. Um, and so in recognizing and thinking about anytime you have a child who has an um an unexplained or unanticipated. Excessive immune response, um, it's important to think about this family of diseases. Historically, we've thought of HLH is kind of these two varieties, is a primary HLH or secondary HLH. I think we're coming to appreciate that there's a lot of overlap between these. Historically, if it was a child, an infant that had disease, we thought it was primary, an older child, we thought secondary. Um, interestingly, um, the oldest patient in the literature with homozygous peripheral mutations presented at age 72. And indeed, as this entity is being recognized. More commonly by um our colleagues in internal medicine, we're realizing that primary HLH can happen um in older children, teenagers and adults. And so it's important to look for an underlying cause because that can change your therapy. Um, Doctor Allen's group at Texas Children's Hospital sequenced a large number of patients, um, that presented with an HLH-like phenotype, and they found a much broader, um, panel of mutations than had initially been. Um, appreciated in the literature. So in addition to the familial genes, um, they also identified primary immunodeficiency associated genes, um, and, um, several other immune immunologically relevant, um, pathways. And so the current um thinking in the field has really moved to this idea of gigenic um uh genetic contributors to HLH where you may have mutations in a couple of different pathways in terms of cytolytic granule, um, uh, production or movement within. The cell or periphering killing and those, if they're um digenic, meaning you have different mutations that are both heterozygous, it may cripple the pathway but not completely um eliminate its function. And these are patients that may present um without quite full-blown um HLH but definitely hyperinflammation um and may be predisposed because this pathway is important for eliminating malignancies, um, uh, to lymphomas in future, um, and adult years. And so this is the approach we currently use to think about this. Low risk HLH patients, meaning they have no associated mutations, require a very large antigenic load in order to develop an HLH phenotype. Patients who have classic um familial HLH nonsense biolylic mutations need very little infection or antigenic stimulation um to develop HLH and those are the patients that often present early. In the middle are patients who have one or two mutations or maybe hypomorphic mutations. It may take more for them to develop HLH, um, but I think anytime you have a child who has an unusual presentation of a common childhood illness, thinking about whether they have a predisposition to this disease, um, is critical, um, in pediatrics. And so just to summarize, um, we now believe there are multiple pathways to HLH or hyperinflammation. It can be the classic cytolytic defects that I just walked you through. Um, more recently emerging category are inflammosomopathies. Inflammosomes are a component of immune cells that are important for also terminating immune responses. This includes XIAP and NLRC4. Um, and this pathway, You get very high levels of IL-18. Um, you also see this in patients who have autoimmune, um, disease and what what we call HLH macrophage activation syndrome. Um, this pathway leads to uncontrolled persistent activation of lymphocytes, um, and whether you come from this direction or this direction or you just have lots of antigen like we see when we use um CAR T cells, um, to treat patients with leukemia, you get, um, very high levels of interferon gamma that leads to macrophage activation and production of cytokines including IL-6, IL-10, IL1 beta, and TNF alpha. And so this really gets this feed forward loop. Um, of hyperinflammation. Oops. So, um, what do we do about that? Um, I do think it's important to think about a large antigenic load and acquired forms or as triggers, um, in patients who have a familial predisposition. Um, infection is the most common, um, and it really, any infection you can think of has probably been reported in the literature. The most common are herpes viruses, uh, the hepatitis influenza, and, you know, And I think there's starting to be reports around the country um of HLH being triggered by measles, um, bacteria, microbacteria, parasites, particularly leshmania and, um, uh, uh, is a com um one that is common in many parts of the world, um, and then fungus. You always need to think about malignancy in these patients and often that can be masked, um, or difficult to find and then to also think about rheumatologic disease. So how do we approach these patients? The first step is to recognize hyperinflammation. Um, uh, Doctor William Temple, um, Ben Wong, and Ben Wong, um, and I, um, developed a standard operating procedure that we're happy to share, um, to really help, um, practitioners in our setting think about how, um, these patients. So the first step is to recognize hyperinflammation. Historically, and this is a consult that I get frequently, like they've only met 4 out of 8 criteria of HLH is it HLH and so, um, I think these uh diagnostic criteria can be helpful, but they can also sometimes limit um people from taking the step to appropriate care for a patient. These were designed as um study criteria, um, inclusion criteria for um the HLH 94 and 2004 um clinical trials. And so I think remembering that um these are um more guidelines can be helpful. Um, they include either a molecular diagnosis of um genetic HLH which almost um never unless you have a family history, do you have a presentation or five of eight of these criteria. So fever, Splenomegaly, cytopenia of two or more cell lines, hypertriglyceridemia or hypophyrogeninemia, hemophagocytosis, and elevated ferritin over 500, elevated soluble um CD25 which is the IL. 2 receptor and lower absent in case cell activity. I will note that the only place to get this tested, um, number 8 is in Cincinnati. It's a very poor test with very poor sensitivity and specificity, and they actually don't send it in their setting, um, and so we generally do not look at this in, um, uh, currently, um, in our practice. Um, there have been since the HLH 94 and 04 criteria, there have been additional um scoring criteria that have been put forth by different organizations. I think it's helpful to remember that this is not a checklist, uh, um, but really just guidelines to help you think of About hyperinflammation. Um, the important, um, additions in this are, um, uh, liver irritation and, um, uh, activation or, um, elevation of liver enzymes which are commonly affected in patients who have hyperinflammation. I think more helpful is to actually appreciate that the signs and symptoms of HLH are really sequelae of the cytokine storm and mapped to specific elevations of specific cytokines. So the fever most likely is really driven by high levels of IL1 and IL 6, which come from macrophages and neutrophils. The pancytopenia in late stages is due to hemophagocytosis, but in early stages. Actually, um, more likely due to, um, suppression of, um, uh, blood, uh, cell formation, um, by both TNF alpha and interferon gamma which will, um, inhibit, um, hematopoiesis at the stem cell and early progenitor stages. The high triglycerides are due to high levels of TNF alpha inhibiting lipoprotein lipase. The low fibrinogen, and I find this actually one of the most helpful, um, Clues to HLH um is due to activated macrophages leading to um production um and release of plasminogen activators which leads to hyperfibrinolysis. The high soluble IL2. Aisle 2, sorry. Um, is due to activated lymphocytes that shed off a T cells, so that's probably the most specific of these criteria. And then the organ dysfunction and sometimes neurologic symptoms are really due to activation of macrophages within those tissues, infiltration by lymphocytes, and subsequent damage. So when should you think about HLH? Patients with prolonged fever, patients with unexplained liver inflammation, patients with coagulopathy, particularly a low fibrogengen, cytopenias, particularly low platelets, um, because they have the shortest half-life can be, um, a helpful marker to trend, high ferritin, um, and or an elevated soluble IL-2 receptor. And then patients with a lymphoid malignancy, especially um wanna think about this. If the soluble IL-2 receptor is um out of proportion and elevated relative to the ferritin, think lymphoid malignancy in those patients. And then, in general, any sick patient without a good explanation at any age, HLH should at least be in the differential. A few other clues include family history, unexplained death in childhood, unexplained liver disease. We've actually had a couple of patients at HL at UCSF where HLH was missed in the initial child who um had liver disease, got a transplant, and then a subsequent either um presented with another bout of. age or had a sibling who presented similarly and so thinking about that in that population is important. And then a family history of lymphoid malignancies, particularly in males, triggers you to think about um X-linked lympholiferative disease. Inflammatory bowel disease and um infants, toddler boys also um should be a trigger to think about XLP. Um, and then I think serial assessment of laboratory indicators is very helpful in these, um, patients. Um, either declining fibrinogen or increasing ferritin make me nervous. A low sed rate with a high, um, CRP also makes me anxious. The sed rate will be low because you have, um, decreased fibrinogen, um, but you'll see inflammation from the high CRP. I want to say a couple of words about ferritin. It is an acute phase reactant, um, and very non-specific, but it is a good test of macrophage, um, activation or a sign of macrophage activation. There was a retrospective review over 2 years of all patients with ferritins greater than 500 at Texas Children's Hospital. They had over 1000 samples and 30,000 admissions. Um, 10 patients had HLH and 320 were non-HLH, um, and they assigned in this study patients to diagnostic. Categories by their primary discharge diagnosis, um, and then looked further into the ones where, um, there was either HLH or it was unknown but had high levels. And I think this is quite striking data. Patients who had, um, an, uh, ferritin of greater than, um, 20,000 generally fell into that HLH or unknown, um, category. Um, moreover, Um, if you looked at the peak ferritin, the one when you get over that, um, 15 to 20,000 range, all of those patients were HLH. There's really not many other things that can give you an HLH and that type of, um, phenotype, um, other than hyperinflammation and In terms of the predictive value, um, the emission ferritin was 74 to 83%, um, accurate. The maximum ferritin actually had 85 to 95% ferritin or accuracy, particularly if it was over 10,000, um, and if you added in a fever, you get to 90%. 8% um specificity as well as very good um sensitivity. And then um they also very importantly showed in this paper that the rate of change in the ferritin was also indicative of HLH. In non-HLH it'll be kind of um consistently elevated, um, but in HLH you'll see rapid changes and this can be very helpful to trend um and to um determine whether or not your interventions are being helpful. There are some clues to that it might not be HLH leukocytosis, absence of cytopenias, especially if you have a high platelet count, that's less likely to be HLH. It may be inflammation from another etiology, but probably not HLH. A high fibrinogen, a normal soluble IL-2 receptor. Since T cells are central to the pathogenesis of this disease, having a high, um, soluble IL-2 receptor makes it less likely. Uh, or having a normal soluble IL-2 receptor, um, makes it much less likely since that's really a signal of activated T cells. Positive COMs, lymphadenopathy, normal liver functions, and a high sed rate also, um, can, um, cast doubt that this is, um, HLH. So this is, um, I think a useful approach to the patient with suspected hyperinflammation, um, you know, so clinical signs and symptoms that make us think about HLH, a previous family history, um, is important, um, in those patients, we wanna do an evaluation for malignancy, rheumatologic disease, infection, and primary immunodeficiency, and then to really look at the inflammatory markers. If the ferritin or soluble IL-2 receptor are not elevated, it's unlikely to be HLH other than isolated CNS disease in the context of HLH which can happen, present as confusion, but have normal systemic markers. If the inflammatory markers are abnormal, then you want to start going down um the approach of is this HLH and I'll go into that in more detail in a moment. So, first up, recognize hyperinflammation. We see hyperinflammation in our patient, what should we do next? Um, Uh, the next step is really to identify and treat the trigger. Um, people often, and we actually wrote this SOP because people often, um, jump down to treating, but, um, it's really important to understand why this happens. HLH even in familial situations or in the myriad models where you can engineer um a family predisposition syndrome to HLH does not occur spontaneously. You have to infect those mice or give them cancer. Um, same thing with patients, that it doesn't occur spontaneously and so you always want to look for a, a trigger, um, with every flare. And if, you know, sometimes I'll get calls about patients who were doing great and all of a sudden their ferritin just went back up to 40,000. In those cases, it's important to send all of the viral studies and to think about what a new trigger might be. Um, and so when looking for the trigger, you wanna think about infection, malignancy, a sulfa antigen. Um, and I really think about treating the trigger and why I have it before any other therapy as turning off the bathwater. If you treat with immunosuppressants, which you don't treat the trigger, um, the water's just gonna keep flowing out of the bathtub. So, Found your trigger or at least have done your best to look for it and sometimes you can't find anything, but it's important to look exhaustively for that. Third step is really to calm the hyperinflammation. I think of treating HLH in two phases. The first phase being induction therapy. We want to gain control of the damaging immune hyper activation, treat the underlying infectious trigger, and limit organ damage and mortality. The second step is really the definitive therapy, and this is only when indicated, um, and its goal is really to prevent potentially um fatal future recurrences by correcting the underlying immune defect with the transplant. So this is the current um approach to HLH therapy. Uh, it involves high-dose steroids, um, twice weekly and then once weekly etoposide. And if a patient has CNS um manifestations, interthecal methotrexate and hydrocortisone, once their immune system has calmed down and, um, ensuring they don't have a coagulopathy and it's safe to do a lumbar puncture. Um, this was based on HLH 94. The HLH 2004 study, um, tested whether cyclosporin in a, um, would make a difference in a randomized fashion, and there was actually no difference, but more seizures in the cyclosporin arm, so we do not use that in our practice. Um, the goal of this therapy is really to um control hyperinflammation. Historically, um, People follow this similar to what we do in oncology as a protocol and you had to get every single dose and on time. I think over the last decade, there's been um a shift in this thinking and that what we really need to do, this isn't an underlying oncologic Disease, it's really hyperinflammation and so you want to look at the patient and treat them appropriately. Some patients will be controlled on steroids alone, and most patients will actually not need 8 weeks of the Topiside. And so we've really moved towards Treating patients based on um what they um their uh level of inflammation dictates. With that said, the overall outcomes for patients with HLH have not improved all that much until very recently, um, and are not great. Um, you know, we can cure, um, generate long-term cures, generate with transplant in about, um, 60 to 70% of patients, but that means that there's a lot of patients, um, that we need to develop better approaches or, um, be able to manage, um, their reactivation or persistence of the disease better. So what can we use to treat HLH in addition to, you know, big gun steroids and etoposide? Um, if we think about the pathophysiology, there's a whole lot of, um, different, um, approaches that are currently being tested, and I think it's an exciting time, um, for these patients. Um, these include agents. Such as tocilusumab or cetuximab that inhibit IL-6 and Tannercept that inhibits TNF alpha, um, uh, anakinra, um, which can affect, um, IL-1. Um, there are agents that may be helpful for the tissue in um injury standpoint. Iapalumam blocks interferon. Gamma JAC inhibitors, um, and I'll go into more detail and these can affect, um, cytokine signaling pathway, um, and act at both the T cell and the macrophage level. If it's an EBV infection, we have some possibilities and so it's an exciting time, I think, in terms of new approaches for, um, these patients. So, um, a few words on emapalumam, um, which is, um, an interferon gamma blockading, um, antibody. It acts both on circulating interferon gamma as well as interferon gamma that is bound to the receptor. Um, patients, um, who, uh, in the pivotal trial, um, this was a single arm, um, phase 12 study, um, who failed HLH conventional therapy could receive this and the Computer, it's got a mind of its own, um, and the patients, um, had an overall 12 month survival of about 73%, so still not 100%, um, but certainly active in a number of patients. If you, um, looked at, um, uh, all treated patients, again it was about 70%, and, um, if patients could get to transplant, they actually did quite well. A second possibility um is anakinra, which is an IL-1 receptor antagonist. There are limited case series showing response. Um, it is relatively benign in that it doesn't increase your infection risk, um, and will not mask a, um, malignancy while you're, um, waiting to get a, a PET CT, um, to look at that, which is different from, um, using, um, high-dose steroids or etoposide. It also crosses the blood-brain barrier and so it can be excellent for patients with CNS. Um, and we have had good luck, um, using this as a steroid sparing agent, um, or as, um, a way to get patients off of steroids while we're bridging them to transplant, um, particularly those, um, kids who have isolated CNS disease. So, um, another useful agent to think about. Rexalitinib has also recently emerged on the scene. This is a potent um reversible inhibitor of JAK-12 um signaling, which is the key regulator of cytokine signaling. Um, it, um, is a pathway that is used by multiple different cytokines, so it can affect both the T cells and the macrophages and neutrophils. It is an oral agent and has excellent bioavailability, but you need to make sure your patient can actually absorb, um, a drug before you give this. Um, it has a short half-life, um, which allows for dose titration. Um, and probably, um, affects HLH through um multiple different mechanisms. It has been FDA approved, um, for other, um, diseases and has known defined toxicity profiles in children and, um, has, um, been shown to be, um, pretty safe and well tolerated. Um, we are currently testing this agent in the North American Consortium for Histocytosis, um, and I think this is, um, interesting, um, animal data that shows that interferon gamma is crucial for initiating HLH, um, and, um, and, and this and this experiment. They took mice that were predisposed to HLH by um having perfin mutations and then bred them with animals that lack different cytokines. And what they found is that um interferon gamma is really the key driver um in um helping these um animals survive when you give them a trigger to get them HLH. However, there's been subsequent studies that have shown that other um pathways are still important. So interferon gamma deficient mice who have a predisposition to HLH will still die with LCMD infection, um, and, um, other, um, cytokines um can actually be more protective in these animals. So, um, it's not, um, a complete interferon gamma-only driven disease. Yeah, um, studies have also shown that, um, neutrophils are important in this disease. So in this study, um, they used animals that, um, had a peripheral mutation and, um, gave them, um, CMV infection to trigger disease. Um, if you didn't give them any intervention, the animals would die. If you treated them only with an anti-interferon gamma antibody, about half of the mice. Um, succumb to disease. However, if you gave them ruxalitinib, you could rescue the animals. And what was interesting is that it really seemed to be, um, the effect of ruxalitinib on inner, um, the neutrophils that was important because if you, um, took away neutrophils with an antibody and these um mice, um, some of them would survive about the same numbers the interferon gamma might, um. Uh, mice that received interferon gamma. If you gave interferon gamma plus, um, uh, the antineutrophil antibody, then you actually got quite nice responses in these animals. And so, um, Ruxolitinib, um, is an agent that certainly deserves more testing in children. Um, we also have data, um, and this comes from my own laboratory that, um, uh, Affecting um jacksat signaling with Rexylitinin can um um maybe protect animals by synergizing with the steroids. So we have found that if you give um T cells, um, uh, if you grow T cells from um a human being, a normal human being in the presence, um, Of increasing levels of cytokine, they become resistant in this top line, um, to killing with dexamethasone and so even at very high doses and so, um, from that, and that's due to the fact that these cells actually in the presence of steroids increase a pro survival protein called BCL2. Um, and, um, you can reverse this effect, um, in the context of, um, rexalitinib. And so this is just nicely showing this that when you have cells that are grown in the presence of IL-2, um, which we know is elevated in patients with HLH, they're resistant to dexamethasone, but if you give even tiny levels, um, of rexalitinib, you can reverse this resistance and Make them more sensitive. Um, and so we are now, um, actually testing this in the context of a clinical trial. Um, uh, there's a group in China that recently reported, um, a lovely study showing, um, uh, that this seems to also be active in humans and that if you give roxalutinib, you can definitely improve the outcomes of these patients to up to 80%, which is much better than any of the historical studies. Um, and so we do have this study open, um, at our center, um, and, um, are starting to, um, use this approach in children. The next step, once you've gotten the patient stabilized, the inflammation um calmed, is to determine if there's an underlying defect in the immune system, so that if there is, you can prevent future episodes of HLH by replacing the immune system. So, the approach that we usually take for this is to do what we call rapid functional screening. So we um send cells for flow cytometry for perfarin, CD107A mobilization, SAP and XIAP which um are both the, of the markers for the X-linked lymphoroliferative disorders. Um, If the perfin is decreased, we'll then um sequence for perfin mutations. If the CD107A is decreased, that actually picks up almost all of the, and I'll show you how that assay works, um, pathway, uh, all of the different pathways or mutate proteins that are mutated in the pathway for cytotic granule release. Um, and then, um, the SAP and XIAP will tell you about the XL1, P1 and 2, linked, um, disorders. If we see any of these functional tests abnormal, then we will, um, because genotype dictates phenotype, we'll do confirmatory genetic testing. It's also important to have this information so that if we have to do a transplant on a patient, we wanna make sure that any sibling or parent donors do not um carry the same mutation, um, before, um, choosing a donor for transplant. And so this is looking at the flow cytometry based assay for looking at perforin, um, so in a normal person, um, when you activate their cells, they have an increase in this expression of perforin, and a patient who has a perforin deficiency that um increase in perforin does not happen. Um, and then this is the CD107A, um, uh, degranulation assay. So CD107A normally lives on the cytolytic granules. If you stimulate those cells, the cytolytic granules fuse with the cell surface and you get this big increase in CD107A expression. And so this will pick up any defect in the pathway to getting these granules to the cell surface. Um, and so this is how this looks. So this is the controls. When you stimulate them, you get all the CD107A on the cell surface and it doesn't happen in a patient who has a known mutation, um, in on 13, which is one of the pathways in them. If you can determine that a patient has, um, HL uh an HLH genetic mutation, then the next step is really to um replace the immune system. Um, and, um, I think there's always controversy in the field over who to transplant. Um, I think that the simple litmus test is to simply ask the question, would this patient be better, safer, or healthier with a different immune system? Is their own immune system helping or hurting them? Um, the current recommendations in the literature are, um, to transplant patients with familial HLH, including CMS only disease, to transplant patients who have recurrent or refractory HLH, even if you can't find the gene defect, um, and then to consider transplantation in patients who have abnormal functional testing, even if we can't yet find the disease with the disease um gene defect with our current sequencing technology. Um, if they have um recurrent self-damaging inflammation. Um, so this is the approach that we take. Um, when we have a patient with HLH, we will start to do the testing. Um, and then we give enough therapy to keep their disease in control and to prevent, um, damage until we can get them to transplant. And we generally try to get them to transplant within, um, Uh, a couple of months once their immune system has calmed down. Sometimes we can't get the immune system completely calm and, um, the consensus in the field is those patients are good to take the transplant regardless. And that's really based on this finding that the earlier you Transplant patients, the better they do, um, because they have less, um, organ damage. Um, and, um, just to say that transplanting HLH is more challenging than many other immune defects because the inflammation and the predisposition to organ damage. So how do we transplant these patients? Um, Uh, well, I appreciate this audience is primarily, um, general pediatricians. I do think it's helpful to understand what we think about as transplanters, um, in case one of your patients has to go down this pathway. What we're really doing, I think from a transplanter perspective is trying to balance graft persistence and survival with toxicity of the transplant conditioning. There are essentially 3 different types of conditioning regimens we can do. We can do what we call MAC or myeloablative conditioning. This is very aggressive chemotherapy, often with total body irradiation, and the goal is to completely eliminate the bone marrow in the patient, so there's no chance of autologous recovery. Oops, apologize, my computer has a mind of its own today. Um, the idea is that you prevent rejection by removing host, um, uh, host graft versus host potential by opening up the marrow niches. Um, more recently, additional approaches have been developed, including, um, RTC, which is reduced toxicity myeloablative conditioning where we use, um, modern approaches to, um, to target our diseases so that we get myeloablation but less organ toxicity, um, and there are different regimens that can be used for that. And then the third approach is reduced intensity conditioning. In patients with HLH we're not trying to eliminate malignancy, we just want to give them an immune system. And so the idea is that if you um do less um intense um therapy just to make space for the new um cells that might be sufficient. So what does the data tell us? Um, there has not been a randomized control trial comparing these different approaches. Um, The um CIBMTR, which is um the International Cooperative for Transplant and um Patients, did compare a retrospective comparison of 261 HLH patients. 96 got myeloblade of very intense conditioning, 28 got Reduced toxicity conditioning with three drugs called fludarabine, melphalan, and thiotepa. Um, and 14 patients got targeted, um, reduced targeted conditioning with busulfan and fludarabine, and then 123 patients actually got reduced intensity conditioning. And these were the key results. So the patients who got flubu, which is the intermediate, Um, uh, targeted conditioning actually had the best overall and event-free survival. That was followed by the patients who got also reduced, um, intensity therapy, um, and then the patients who got the most intense myeloablative actually did quite poorly, mainly due to toxicity, and the patients who got the reduced intensity also did more poorly, um, um, often due to graft failure. And so, um, this is graph failure is shown here, um, you have the least, um, failure if you use flubu, um, and the most if you use the reduced intensity, um, conditioning with flu fludarabine and mealfolan, um. And so, kind of looking at all of that data, the recommendation consensus from the authors of the paper were that a flumel thiotepa regimen might optimize the balance between toxicity and ensuring sustained donor engraftment for HLH, um. Our feeling at UCSF because we are very fortunate to have um an amazing pharmacist, Janelle on Boyle, who can do targeted um dosing for us is that we've had since we've moved to targeted in dosing and added in a drug called elantuzumab, we've had very Very few, um, uh, graft failures, um, and we also prophylax our patients for liver injury with, um, a drug called defibritide, um, and we use an, an anti um cytokine cocktail on day zero to also calm down their immune system. And so this has led to very good outcomes for these children, but certainly, um, more study is needed and, and really at an international level given the rarity of this disease. So, in the last um few minutes before questions, um, I just wanna talk a little bit about where the field is moving to and the unmet needs and HLH. So, you know, we know to treat the trigger, to calm the hyperinflammation, and that ideally you wanna replace the defective immune system. Historically, survival has been stuck at 60% even with um to 70% even with emalumab, um Ritux uh roxalitinib, the JAK inhibitor might get a A little higher. The deaths generally are due to inability to control hyperinflammation or secondary infections due to profound immunosuppression. We know from animal studies that you only need about 30% functional T cells in order to calm the inflammation. And so this raises the very intriguing idea, could correcting corrected T cell therapy alone be sufficient for at least a subset of these patients. Um, Very excited, um, in that, um, we, um, are gonna be testing that at UCSF. Um, Jennifer Doudna, um, leads the Innovative Genomics Institute and, um, she was the recipient of the Nobel Prize for developing CRISPR cast editing where we can go in and fix, um, very precisely gene defects. And so, um, we're working with, um, David Wynn's lab, um, um, at the IGI. Um, he's also an infectious disease specialist in internal medicine at UCSF to really try to, to test this, um, in patients. And so the idea will be to use CRISPR-Cas gene editing to, um, repair the gene defect in, um, patients who have, um, familial HLH, um, and then See if these T cells can sufficiently control the patient, um, either if they have recurrent bouts of this or as a bridge, um, to gene edited, um, hematopoietic stem cells. Um, this approach is very exciting to us and that it may, um, spare patients a lot of the toxicity of transplants and chemotherapy. Um, uh, and the, um, increased infection risk that comes with, um, profound immune suppression. So stay tuned. This is in the early stages. We're hoping to be, um, to the point of being able to treat patients in about 3 years. So, takeaways, um, HLH is a syndrome of excessive inflammation. There can be many different triggers. Always think about autoimmunity, infection, and malignancy. You need to recognize and accurately diagnose HLH, treat the trigger, or you just keep having, um, Uh, firing, um, the, um, inflammation, calm the hyperinflammation, um, and I think there really is a move away from following a protocol, but rather treating the patient and giving them only the amount of anti-inflammatories that are necessary to, um, keep them safe. And then ultimately replacing the immune system when appropriate. Um, and in italics, you know, I think we need more data to really know how to, um, and clinical trials are necessary to best treat these patients, um, but I think it's an exciting time and that there are new approaches on the horizon. Um, I want to thank a number of collaborators, particularly from the, um, Nacho Consortium, um, and patients and families, um, and then, um, oops. Uh, I'm always happy to talk to, um, referring physicians, um, about these patients, and we do have an immuno, uh, dysregulation conference every other Thursday. Um, we always wel um where we present our own, um, patients who are complicated in a multidisciplinary setting, and, um, we occasionally will have, um, teams from outside institutions present at this conference just to get, um, additional But, um, I find it takes a village to really think carefully about these kids and the best approaches. So, um, always can feel, um, free to email us, um, and we're happy to add that to our, um, uh, conference schedule. And we can also pull this team together, um, on very short notice, um, it's usually Friday afternoons cause that's when these kids often present, um, uh, to discuss, um, therapeutic approaches for them. And I will stop there.
