Innate acting memory Th1 cells modulate heterologous diseases.

Through immune memory, infections have a lasting effect on the host. While memory cells enable accelerated and enhanced responses upon rechallenge with the same pathogen, their impact on susceptibility to unrelated diseases is unclear. We identify a subset of memory T helper 1 (Th1) cells termed innate acting memory T (TIA) cells that originate from a viral infection and produce IFN-γ with innate kinetics upon heterologous challenge in vivo. Activation of memory TIA cells is induced in response to IL-12 in combination with IL-18 or IL-33 but is TCR independent. Rapid IFN-γ production by memory TIA cells is protective in subsequent heterologous challenge with the bacterial pathogen Legionella pneumophila. In contrast, antigen-independent reactivation of CD4+ memory TIA cells accelerates disease onset in an autoimmune model of multiple sclerosis. Our findings demonstrate that memory Th1 cells can acquire additional TCR-independent functionality to mount rapid, innate-like responses that modulate susceptibility to heterologous challenges.

Intestinal cDC1s provide cues required for CD4+ T cell-mediated resistance to Cryptosporidium.

Cryptosporidium is an enteric pathogen and a prominent cause of diarrheal disease worldwide. Control of Cryptosporidium requires CD4+ T cells, but how protective CD4+ T cell responses are generated is poorly understood. Here, Cryptosporidium parasites that express MHCII-restricted model antigens were generated to understand the basis for CD4+ T cell priming and effector function. These studies revealed that parasite-specific CD4+ T cells are primed in the draining mesenteric lymph node but differentiate into Th1 cells in the gut to provide local parasite control. Although type 1 conventional dendritic cells (cDC1s) were dispensable for CD4+ T cell priming, they were required for CD4+ T cell gut homing and were a source of IL-12 at the site of infection that promoted local production of IFN-γ. Thus, cDC1s have distinct roles in shaping CD4+ T cell responses to an enteric infection: first, to promote gut homing from the mesLN, and second, to drive effector responses in the intestine.

Anti-PD-1 cis-delivery of low-affinity IL-12 activates intratumoral CD8+T cells for systemic antitumor responses.

Immune checkpoint blockade (ICB) therapies function by alleviating immunosuppression on tumor-infiltrating lymphocytes (TILs) but are often insufficient to fully reactivate these dysfunctional TILs. Although interleukin 12 (IL-12) has been used in combination with ICB to improve efficacy, this remains limited by severe toxicity associated with systemic administration of this cytokine. Here, we engineer a fusion protein composed of an anti-PD-1 antibody and a mouse low-affinity IL-12 mutant-2 (αPD1-mIL12mut2). Systemic administration of αPD1-mIL12mut2 displays robust antitumor activities with undetectable toxicity. Mechanistically, αPD1-mIL12mut2 preferentially activates tumor-infiltrating PD-1+CD8+T cells via high-affinity αPD-1 mediated cis-binding of low-affinity IL-12. Additionally, αPD1-mIL12mut2 treatment exerts an abscopal effect to suppress distal tumors, as well as metastasis. Collectively, αPD1-mIL12mut2 treatment induces robust systemic antitumor responses with reduced side effects.

The alteration of NK cells phenotypes related to the functions and dengue disease outcomes.

Natural killer cells (NK cells) are the front line of immune cells to combat pathogens and able to influence the subsequent adaptive immune responses. One of the factors contributing to pathogenesis in dengue hemorrhagic fever (DHF) disease is aberrant immune activation during early phase of infection. This study explored the profile of NK cells in dengue infected pediatric patients with different degrees of disease severity. DHF patients contained higher frequency of activated NK cells but lower ratio of CD56dim:CD56bright NK subsets. Activated NK cells exhibited alterations in several NK receptors. Interestingly, the frequencies of NKp30 expressing activated NK cells were more pronounced in dengue fever (DF) than in DHF pediatric patients. In vitro functional analysis indicated that degranulation of NK cells in responding to dengue infected dendritic cells (DCs) required cell-cell contact and type I IFNs. Meanwhile, Interferon gamma (IFN-γ) production initially required cell-cell contact and type I IFNs followed by Interleukin-12 (IL-12), Interleukin-15 (IL-15) and Interleukin-18 (IL-18) resulting in the amplification of IFN-γ producing NK cells over time. This study highlighted the complexity and the factors influencing NK cells responses to dengue virus. Degree of activation, phenotypes of activated cells and the crosstalk between NK cells and other immune cells, could modulate the outcome of NK cells function in the dengue disease.

IL-12 Mediates T-bet-Expressing Myeloid Cell-Dependent Host Resistance against Toxoplasma gondii.

To defend against intracellular pathogens such as Toxoplasma gondii, the host generates a robust type 1 immune response. Specifically, host defense against T. gondii is defined by an IL-12-dependent IFN-γ response that is critical for host resistance. Previously, we demonstrated that host resistance is mediated by T-bet-dependent ILC-derived IFN-γ by maintaining IRF8+ conventional type 1 dendritic cells during parasitic infection. Therefore, we hypothesized that innate lymphoid cells are indispensable for host survival. Surprisingly, we observed that T-bet-deficient mice succumb to infection quicker than do mice lacking lymphocytes, suggesting an unknown T-bet-dependent-mediated host defense pathway. Analysis of parasite-mediated inflammatory myeloid cells revealed a novel subpopulation of T-bet+ myeloid cells (TMCs). Our results reveal that TMCs have the largest intracellular parasite burden compared with other professional phagocytes, suggesting they are associated with active killing of T. gondii. Mechanistically, we established that IL-12 is necessary for the induction of inflammatory TMCs during infection and these cells are linked to a role in host survival.

Mesothelin CAR-T cells expressing tumor-targeted immunocytokine IL-12 yield durable efficacy and fewer side effects.

Chimeric antigen receptor (CAR)-modified T cell therapy has achieved remarkable efficacy in treating hematological malignancies, but it confronts many challenges in treating solid tumors, such as the immunosuppressive microenvironment of the solid tumors. These factors reduce the antitumor activity of CAR-T cells in clinical trials. Therefore, we used the immunocytokine interleukin-12 (IL-12) to enhance the efficacy of CAR-T cell therapy. In this study, we engineered CAR-IL12R54 T cells that targeted mesothelin (MSLN) and secreted a single-chain IL-12 fused to a scFv fragment R54 that recognized a different epitope on mesothelin. The evaluation of the anti-tumor activity of the CAR-IL12R54 T cells alone or in combination with anti-PD-1 antibody in vitro and in vivo was followed by the exploration of the functional mechanism by which the immunocytokine IL-12 enhanced the antitumor activity. CAR-IL12R54 T cells had potency to lyse mesothelin positive tumor cells in vitro. In vivo studies demonstrated that CAR-IL12R54 T cells were effective in controlling the growth of established tumors in a xenograft mouse model with fewer side effects than CAR-T cells that secreted naked IL-12. Furthermore, combination of PD-1 blockade antibody with CAR-IL12R54 T cells elicited durable anti-tumor responses. Mechanistic studies showed that IL12R54 enhanced Interferon-γ (IFN-γ) production and dampened the activity of regulatory T cells (Tregs). IL12R54 also upregulated CXCR6 expression in the T cells through the NF-κB pathway, which facilitated T cell infiltration and persistence in the tumor tissues. In summary, the studies provide a good therapeutic option for the clinical treatment of solid tumors.

Interleukin-12: Structure, Function, and Its Impact in Colorectal Cancer.

Interleukin 12 (IL-12) is a heterodimer consisting of 2 subunits, p35 and p40, with unique associations and interacting functions with its family members. IL-12 is one of the most important cytokines regulating the immune system response and is integral to adaptive immunity. IL-12 has shown marked therapeutic potential in a variety of tumor types. This review therefore summarizes the characteristics of IL-12 and its application in tumor treatment, focusing on its antitumor effects in colorectal cancer (CRC) and potential radiosensitization mechanisms. We aim to provide a current reference for IL-12 and other potential CRC treatment strategies.

Anti-Interleukin-23 Autoantibodies in Adult-Onset Immunodeficiency.

BACKGROUND: Autoantibodies against interleukin-12 (anti-interleukin-12) are often identified in patients with thymoma, but opportunistic infections develop in only some of these patients. Interleukin-12 (with subunits p40 and p35) shares a common subunit with interleukin-23 (subunits p40 and p19). In a patient with disseminated Burkholderia gladioli infection, the identification of both anti-interleukin-23 and anti-interleukin-12 prompted further investigation. METHODS: Among the patients (most of whom had thymoma) who were known to have anti-interleukin-12, we screened for autoantibodies against interleukin-23 (anti-interleukin-23). To validate the potential role of anti-interleukin-23 with respect to opportunistic infection, we tested a second cohort of patients with thymoma as well as patients without either thymoma or known anti-interleukin-12 who had unusual infections. RESULTS: Among 30 patients with anti-interleukin-12 who had severe mycobacterial, bacterial, or fungal infections, 15 (50%) also had autoantibodies that neutralized interleukin-23. The potency of such neutralization was correlated with the severity of these infections. The neutralizing activity of anti-interleukin-12 alone was not associated with infection. In the validation cohort of 91 patients with thymoma, the presence of anti-interleukin-23 was associated with infection status in 74 patients (81%). Overall, neutralizing anti-interleukin-23 was detected in 30 of 116 patients (26%) with thymoma and in 30 of 36 patients (83%) with disseminated, cerebral, or pulmonary infections. Anti-interleukin-23 was present in 6 of 32 patients (19%) with severe intracellular infections and in 2 of 16 patients (12%) with unusual intracranial infections, including Cladophialophora bantiana and Mycobacterium avium complex. CONCLUSIONS: Among patients with a variety of mycobacterial, bacterial, or fungal infections, the presence of neutralizing anti-interleukin-23 was associated with severe, persistent opportunistic infections. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Murine cytotoxic CD4+ T cells in the tumor microenvironment are at a hyper-maturation stage of Th1 CD4+ T cells sustained by IL-12.

The roles of tumor-infiltrating CD4+Foxp3- T cells are not well characterized due to their plasticity of differentiation, and varying levels of activation or exhaustion. To further clarify this issue, we used a model featuring subcutaneous murine colon cancer and analyzed the dynamic changes of phenotype and function of the tumor-associated CD4+ T-cell response. We found that, even at a late stage of tumor growth, the tumor-infiltrating CD4+Foxp3- T cells still expressed effector molecules, inflammatory cytokines and molecules that are expressed at reduced levels in exhausted cells. We used microarrays to examine the gene-expression profiles of different subsets of CD4+ T cells and revealed that the tumor-infiltrating CD4+Foxp3- T cells expressed not only type 1 helper (Th1) cytokines, but also cytolytic granules such as those encoded by Gzmb and Prf1. In contrast to CD4+ regulatory T cells, these cells exclusively co-expressed natural killer receptor markers and cytolytic molecules as shown by flow-cytometry studies. We used an ex vivo killing assay and proved that they could directly suppress CT26 tumor cells through granzyme B and perforin. Finally, we used pathway analysis and ex vivo stimulation to confirm that the CD4+Foxp3- T cells expressed higher levels of IL12rb1 genes and were activated by the IL-12/IL-27 pathway. In conclusion, this work finds that, in late-stage tumors, the tumor-infiltrating lymphocyte population of CD4+ cells harbored a sustained, hyper-maturated Th1 status with cytotoxic function supported by IL-12.

Suppression of Allergic Asthma by Loss of Function of Miz1-mediated Th1 Skewing.

Asthma is the most prevalent chronic respiratory disease worldwide. There is currently no cure, and it remains an important cause of morbidity and mortality. Here we report that lung-specific loss of function of the transcription factor Miz1 (c-Myc-interacting zinc finger protein-1) upregulates the pro-T-helper cell type 1 cytokine IL-12. Upregulation of IL-12 in turn stimulates a Th1 response, thereby counteracting T-helper cell type 2 response and preventing the allergic response in mouse models of house dust mite- and OVA (ovalbumin)-induced asthma. Using transgenic mice expressing Cre under a cell-specific promoter, we demonstrate that Miz1 acts in lung epithelial cells and dendritic cells in asthma. Chromatin immunoprecipitation coupled with high-throughput DNA sequencing or quantitative PCR reveals the binding of Miz1 on the Il12 promoter indicating direct repression of IL-12 by Miz1. In addition, HDAC1 (histone deacetylase 1) is recruited to the Il12 promoter in a Miz1-depdenent manner, suggesting epigenetic repression of Il12 by Miz1. Furthermore, Miz1 is upregulated in the lungs of asthmatic mice. Our data together suggest that Miz1 is upregulated during asthma, which in turn promotes asthma pathogenesis by preventing Th1 skewing through the transcriptional repression of IL-12.

Removal of the Erns RNase Activity and of the 3' Untranslated Region Polyuridine Insertion in a Low-Virulence Classical Swine Fever Virus Triggers a Cytokine Storm and Lethal Disease.

In this study, we assessed the potential synergistic effect of the Erns RNase activity and the poly-U insertion in the 3' untranslated region (UTR) of the low-virulence classical swine fever virus (CSFV) isolate Pinar de Rio (PdR) in innate and adaptive immunity regulation and its relationship with classical swine fever (CSF) pathogenesis in pigs. We knocked out the Erns RNase activity of PdR and replaced the long polyuridine sequence of the 3' UTR with 5 uridines found typically at this position, resulting in a double mutant, vPdR-H30K-5U. This mutant induced severe CSF in 5-day-old piglets and 3-week-old pigs, with higher lethality in the newborn (89.5%) than in the older (33.3%) pigs. However, the viremia and viral excretion were surprisingly low, while the virus load was high in the tonsils. Only alpha interferon (IFN-α) and interleukin 12 (IL-12) were highly and consistently elevated in the two groups. Additionally, high IL-8 levels were found in the newborn but not in the older pigs. This points toward a role of these cytokines in the CSF outcome, with age-related differences. The disproportional activation of innate immunity might limit systemic viral spread from the tonsils and increase virus clearance, inducing strong cytokine-mediated symptoms. Infection with vPdR-H30K-5U resulted in poor neutralizing antibody responses compared with results obtained previously with the parent and RNase knockout PdR. This study shows for the first time the synergistic effect of the 3' UTR and the Erns RNase function in regulating innate immunity against CSFV, favoring virus replication in target tissue and thus contributing to disease severity. IMPORTANCE CSF is one of the most relevant viral epizootic diseases of swine, with high economic and sanitary impact. Systematic stamping out of infected herds with and without vaccination has permitted regional virus eradication. However, the causative agent, CSFV, persists in certain areas of the world, leading to disease reemergence. Nowadays, low- and moderate-virulence strains that could induce unapparent CSF forms are prevalent, posing a challenge for disease eradication. Here, we show for the first time the synergistic role of lacking the Erns RNase activity and the 3' UTR polyuridine insertion from a low-virulence CSFV isolate in innate immunity disproportional activation. This might limit systemic viral spread to the tonsils and increase virus clearance, inducing strong cytokine-mediated symptoms, thus contributing to disease severity. These results highlight the role played by the Erns RNase activity and the 3' UTR in CSFV pathogenesis, providing new perspectives for novel diagnostic tools and vaccine strategies.

Early IFNß secretion determines variable downstream IL-12p70 responses upon TLR4 activation.

The interleukin-12 (IL-12) family comprises the only heterodimeric cytokines mediating diverse functional effects. We previously reported a striking bimodal IL-12p70 response to lipopolysaccharide (LPS) stimulation in healthy donors. Herein, we demonstrate that interferon ß (IFNß) is a major upstream determinant of IL-12p70 production, which is also associated with numbers and activation of circulating monocytes. Integrative modeling of proteomic, genetic, epigenomic, and cellular data confirms IFNß as key for LPS-induced IL-12p70 and allowed us to compare the relative effects of each of these parameters on variable cytokine responses. Clinical relevance of our findings is supported by reduced IFNß-IL-12p70 responses in patients hospitalized with acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or chronically infected with hepatitis C (HCV). Importantly, these responses are resolved after viral clearance. Our systems immunology approach defines a better understanding of IL-12p70 and IFNß in healthy and infected persons, providing insights into how common genetic and epigenetic variation may impact immune responses to bacterial infection.

Attenuated Toxoplasma gondii enhances the antitumor efficacy of anti-PD1 antibody by altering the tumor microenvironment in a pancreatic cancer mouse model.

PURPOSE: To investigate whether attenuated Toxoplasma is efficacious against solid tumors of pancreatic cancer and whether attenuated Toxoplasma improves the antitumor activity of αPD-1 antibody on pancreatic cancer. METHODS: The therapeutic effects of attenuated Toxoplasma NRTUA strain monotherapy and combination therapy of NRTUA with anti-PD-1 antibody on PDAC tumor volume and tumor weight of Pan02 tumor-bearing mice were investigated. We characterized the effects of combination therapy of NRTUA with anti-PD-1 antibody on tumor-infiltrating lymphocytes and tumor-specific IFN-γ by using immunohistochemistry, flow cytometry and ELISA. The antitumor mechanisms of combination therapy of NRTUA with anti-PD-1 antibody were investigated via depletion of CD8+ T cells and IL-12. RESULTS: NRTUA strain treatment inhibited tumor growth in a subcutaneous mouse model of PDAC through activating dendritic cells and increasing CD8+ T cell infiltration in the tumor microenvironment. More importantly, combination therapy of NRTUA with anti-PD-1 antibody elicited a significant antitumor immune response and synergistically controlled tumor growth in Pan02 tumor-bearing mice. Specifically, the combination treatment led to elevation of CD8+ T cell infiltration mediated by dendritic cell-secreted IL-12 and to tumor-specific IFN-γ production in the PDAC tumor microenvironment. Also, the combination treatment markedly reduced the immunosuppressive myeloid-derived suppressor cell population in PDAC mice. CONCLUSION: These findings could provide a novel immunotherapy approach to treating solid tumors of PDAC and overcoming resistance to anti-PD-1 agents in PDAC tumors.

A tumor-specific pro-IL-12 activates preexisting cytotoxic T cells to control established tumors.

It is a challenge to effectively reactivate preexisting tumor-infiltrating lymphocytes (TILs) without causing severe toxicity. Interleukin-12 (IL-12) can potently activate lymphocytes, but its clinical use is limited by its short half-life and dose-related toxicity. In this study, we developed a tumor-conditional IL-12 (pro-IL-12), which masked IL-12 with selective extracellular receptor­binding domains of the IL-12 receptor while preferentially and persistently activating TILs after being unmasked by matrix metalloproteinases expressed by tumors. Systemic delivery of pro-IL-12 demonstrated reduced toxicity but better control of established tumors compared with IL-12-Fc. Mechanistically, antitumor responses induced by pro-IL-12 were dependent on TILs and IFNγ. Furthermore, direct binding of IL-12 to IL-12R on CD8+, not CD4+, T cells was essential for maximal effectiveness. Pro-IL-12 improved the efficacy of both immune checkpoint blockade and targeted therapy when used in combination. Therefore, our study demonstrated that pro-IL-12 could rejuvenate TILs, which then combined with current treatment modalities while limiting adverse effects for treating established tumors.

Cell membrane-anchored and tumor-targeted IL-12 (attIL12)-T cell therapy for eliminating large and heterogeneous solid tumors.

BACKGROUND: Adoptive T-cell transfer has become an attractive therapeutic approach for hematological malignancies but shows poor activity against large and heterogeneous solid tumors. Interleukin-12 (IL-12) exhibits potent antitumor efficacy against solid tumors, but its clinical application has been stalled because of toxicity. Here, we aimed to develop a safe approach to IL-12 T-cell therapy for eliminating large solid tumors. METHODS: We generated a cell membrane-anchored IL-12 (aIL12), a tumor-targeted IL-12 (ttIL12), and a cell membrane-anchored and ttIL-12 (attIL12) and a cell membrane-anchored and tumor-targeted ttIL-12 (attIL12) armed T cells, chimeric antigen receptor-T cells, and T cell receptor-T (TCR-T) cells with each. We compared the safety and efficacy of these armed T cells in treating osteosarcoma patient-derived xenograft tumors and mouse melanoma tumors after intravenous infusions of the armed T cells. RESULTS: attIL12-T cell infusion showed remarkable antitumor efficacy in human and mouse large solid tumor models. Mechanistically, attIL12-T cells targeted tumor cells expressing cell-surface vimentin, enriching effector T cell and interferon γ production in tumors, which in turn stimulates dendritic cell maturation for activating secondary T-cell responses and tumor antigen spreading. Both attIL12- and aIL12-T-cell transfer eliminated peripheral cytokine release and the associated toxic effects. CONCLUSIONS: This novel approach sheds light on the safe application of IL-12-based T-cell therapy for large and heterogeneous solid tumors.

IL12 integrated into the CAR exodomain converts CD8+ T cells to poly-functional NK-like cells with superior killing of antigen-loss tumors.

Chimeric antigen receptor (CAR)-redirected T cell therapy often fails to control tumors in the long term due to selecting cancer cells that downregulated or lost CAR targeted antigen. To reprogram the functional capacities specifically of engineered CAR T cells, we inserted IL12 into the extracellular moiety of a CD28-ζ CAR; both the CAR endodomain and IL12 were functionally active, as indicated by antigen-redirected effector functions and STAT4 phosphorylation, respectively. The IL12-CAR reprogrammed CD8+ T cells toward a so far not recognized natural killer (NK) cell-like signature and a CD94+CD56+CD62Lhigh phenotype closely similar, but not identical, to NK and cytokine induced killer (CIK) cells. In contrast to conventional CAR T cells, IL12-CAR T cells acquired antigen-independent, human leukocyte antigen E (HLA-E) restricted cytotoxic capacities eliminating antigen-negative cancer cells in addition to eliminating cancer cells with CAR cognate antigen. Simultaneous signaling through both the CAR endodomain and IL12 were required for inducing maximal NK-like cytotoxicity; adding IL12 to conventional CAR T cells was not sufficient. Antigen-negative tumors were attacked by IL12-CAR T cells, but not by conventional CAR T cells. Overall, we present a prototype of a new family of CARs that augments tumor recognition and elimination through expanded functional capacities by an appropriate cytokine integrated into the CAR exodomain.

Safety evaluation of ustekinumab for moderate-to-severe ulcerative colitis.

INTRODUCTION: Ustekinumab is a human IgG1 kappa monoclonal antibody that targets the p40 subunit of interleukin (IL)-12 and IL-23 and blocks the binding of these cytokines to the IL-12Rß1 chain of their receptors. Ustekinumab is approved for treating moderate-to-severe ulcerative colitis (UC). AREAS COVERED: We reviewed the mechanism of action, pharmacokinetics, efficacy, and safety of ustekinumab. Future challenges for optimizing UC treatment with ustekinumab are discussed. EXPERT OPINION: Ustekinumab has favorable clinical efficacy and safety profiles for moderately-to-severely active UC. Ustekinumab is the first biologic for targeting IL-12/IL-23 pathways. Therefore, ustekinumab can be a therapeutic option following the failure of other biologics, including anti-tumor necrosis factor-α antagonists and anti-α4ß7 integrin antagonists. However, the positioning of ustekinumab in the therapeutic strategy for UC remains unclear. The efficacy of combinations of ustekinumab and immunomodulators over ustekinumab monotherapy has not been supported in studies. Ustekinumab is a human immunoglobulin G monoclonal antibody with low immunogenicity. Therefore, ustekinumab monotherapy, which should be safe, could be sufficient for treating UC. Further studies are required to understand the efficacy and safety of ustekinumab in patients with UC, particularly in special situations, and to optimize UC treatment with ustekinumab.

Intratumoral expression of IL-12 from lentiviral or RNA vectors acts synergistically with TLR4 agonist (GLA) to generate anti-tumor immunological memory.

Systemic interleukin-12 (IL12) anti-tumor therapy is highly potent but has had limited utility in the clinic due to severe toxicity. Here, we present two IL12-expressing vector platforms, both of which can overcome the deficiencies of previous systemic IL12 therapies: 1) an integrating lentiviral vector, and 2) a self-replicating messenger RNA formulated with polyethyleneimine. Intratumoral administration of either IL12 vector platform resulted in recruitment of immune cells, including effector T cells and dendritic cells, and the complete remission of established tumors in multiple murine models. Furthermore, concurrent intratumoral administration of the synthetic TLR4 agonist glucopyranosyl lipid A formulated in a stable emulsion (GLA-SE) induced systemic memory T cell responses that mediated complete protection against tumor rechallenge in all survivor mice (8/8 rechallenged mice), whereas only 2/6 total rechallenged mice treated with intratrumoral IL12 monotherapy rejected the rechallenge. Taken together, expression of vectorized IL12 in combination with a TLR4 agonist represents a varied approach to broaden the applicability of intratumoral immune therapies of solid tumors.

Clinical and laboratory characteristics of hemophagocytic lymphohistiocytosis induced by Leishmania infantum infection.

BACKGROUND: Visceral leishmaniasis (VL) could progress to secondary hemophagocytic lymphohistiocytosis (HLH), which is a rare but life-threatening condition with poor prognosis. So far, the clinical and laboratory characteristics of VL associated HLH have not been well elucidated. METHOD AND FINDINGS: In this study, we retrospectively analyzed the clinical and laboratory profiles between 17 patients with VL associated HLH and 27 patients with VL alone admitted at the Beijing Friendship Hospital, Capital Medical University from May 2016 to March 2021. In addition to the identification of Leishmania infection, hemophagocytosis was identified in bone marrow in the most cases of VL associated HLH (15/17). The patients with VL associated HLH had higher chances of bleeding, hepatomegaly, thrombocytopenia, hypertriglyceridemia, hyperferritinemia, hypofibrinogenemia, elevated secretion of soluble IL-2 receptor or lower NK cell activity compared to patients with VL only. Furthermore, patients with VL associated HLH had higher inflammation status associated with higher levels of Th1 (TNF-α, IFN-γ, IL-1beta, IL-6, IL-8, IL-12p70), Th2 (IL-4) and Th17 cytokines (IL-17, IL-23) in the peripheral blood, and higher parasite load (qPCR and parasite culture). All 27 VL cases were totally recovered after being treated with Sodium Stibogluconate, five of the 17 patients with VL associated HLH died even after timely treatment with anti-parasite and immunosuppressive chemotherapy. CONCLUSION: Without appropriate treatment, visceral leishmaniosis could develop to secondary HLH. The parasite culturing and qPCR detection of bone marrow samples facilitates the diagnosis of VL associated HLH in addition to other findings of HLH. Prompt treatment with anti-Leishmania and immunosuppressive chemotherapy is critical to reduce the mortality of VL associated HLH.