Melanoma and microbiota: Current understanding and future directions

Over the last decade, the composition of the gut microbiota has been found to correlate with the outcomes of cancer patients treated with immunotherapy. Accumulating evidence points to the various mechanisms by which intestinal bacteria act on distal tumors and how to harness this complex ecosystem to circumvent primary resistance to immune checkpoint inhibitors. Here, we review the state of the microbiota field in the context of melanoma, the recent breakthroughs in defining microbial modes of action, and how to modulate the microbiota to enhance response to cancer immunotherapy. The host-microbe interaction may be deciphered by the use of "omics" technologies, and will guide patient stratification and the development of microbiota-centered interventions. Efforts needed to advance the field and current gaps of knowledge are also discussed.

Learning from the microbes: exploiting the microbiome to enforce T cell immunotherapy

The opportunities genetic engineering has created in the field of adoptive cellular therapy for cancer are accelerating the development of novel treatment strategies using chimeric antigen receptor (CAR) and T cell receptor (TCR) T cells. The great success in the context of hematologic malignancies has made especially CAR T cell therapy a promising approach capable of achieving long-lasting remission. However, the causalities involved in mediating resistance to treatment or relapse are still barely investigated. Research on T cell exhaustion and dysfunction has drawn attention to host-derived factors that define both the immune and tumor microenvironment (TME) crucially influencing efficacy and toxicity of cellular immunotherapy. The microbiome, as one of the most complex host factors, has become a central topic of investigations due to its ability to impact on health and disease. Recent findings support the hypothesis that commensal bacteria and particularly microbiota-derived metabolites educate and modulate host immunity and TME, thereby contributing to the response to cancer immunotherapy. Hence, the composition of microbial strains as well as their soluble messengers are considered to have predictive value regarding CAR T cell efficacy and toxicity. The diversity of mechanisms underlying both beneficial and detrimental effects of microbiota comprise various epigenetic, metabolic and signaling-related pathways that have the potential to be exploited for the improvement of CAR T cell function. In this review, we will discuss the recent findings in the field of microbiome-cancer interaction, especially with respect to new trajectories that commensal factors can offer to advance cellular immunotherapy.

Abstract 5910: Prospective platform to define microbiome correlates of metastasis and therapy resistance in early onset and average onset gastrointestinal cancers

Background: The incidence of early onset (EO) gastrointestinal (GI) cancers prior to age 50 is rising, and the etiology is unknown. The gut microbiome may contribute to GI cancer pathogenesis, though how bacteria drive metastasis and treatment resistance is not known.

Purpose: To define the microbiome contribution to EO-GI cancers and metastasis by analyzing longitudinal samples from previously untreated patients with GI cancers.

Methods: We designed a prospective biospecimen collection platform. We selected patients with newly diagnosed, previously untreated colorectal cancer (CRC) and esophagogastric cancer (EGC). We collected stool, biopsy or surgical tissue, and peripheral blood mononuclear cells (PBMCs) at baseline prior to treatment and at each restaging scan for patients with metastatic disease. For those with locally advanced disease, we collected samples at baseline and after each treatment phase (surgery, radiation, chemotherapy). Stool samples were analyzed using shotgun sequencing. Tissue samples were banked for further analysis. Clinical data was manually curated. Relative abundances of bacteria at the species level were compared between groups. Alpha diversity was calculated using the inverse Simpson index and compared between groups using the Wilcoxon signed-rank test. Beta diversity was analyzed using the Bray-Curtis dissimilarity matrix and compared using PERMANOVA. Multivariate association between species abundance and clinical covariates was performed using MaAsLin2 R package.

Results: We analyzed a total of 150 stool samples from 76 patients (colorectal n=53, esophagogastric n=23), including up to 6 samples from a single patient over time. Mean alpha diversity did not differ significantly by primary site or age at diagnosis in patients with CRC but was higher in stage IV compared with stage I disease (P=0.054). Beta diversity was significantly different between samples from patients with right- compared with left-sided CRC (P=0.005) but did not differ significantly by diagnosis age (<50 vs. > 50). Among those with EGC, mean alpha diversity was not significantly different in samples from patients with esophagus or gastroesophageal junction (proximal) tumors compared with gastric (distal) tumors and did not differ significantly by age group. Beta diversity was significantly different between patients with EGC over 50 compared with those under 50 (P=0.002). When CRC baseline samples were examined, several bacterial species were associated with age <50 at diagnosis, including Streptococcus anginosus group (P=0.001), Solobacterium moorei (P=0.013), and Firmicutes bacterium CAG83 (P=0.016).

Conclusions/Future Directions: Microbiome composition may cluster by primary tumor site and age at diagnosis in patients with previously untreated GI cancers. Functional analysis and is ongoing and will be presented.

Citation Format: Melissa A. Lumish, Asha R. Saxena, Nicholas Waters, Anqi Dai, Saskia Hartner, Teng Fei, Matthew Drescher, Jonathan Bermeo, Dorina Ismailgeci, Maggie Fox, Yelena Y. Janjigian, Luis A. Diaz, Martin R. Weiser, Jonathan Peled, Marcel van den Brink, Karuna Ganesh. Prospective platform to define microbiome correlates of metastasis and therapy resistance in early onset and average onset gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5910.

Impact of TP53 Genomic Alterations in Large B-Cell Lymphoma Treated With CD19-Chimeric Antigen Receptor T-Cell Therapy

PURPOSE

Tumor-intrinsic features may render large B-cell lymphoma (LBCL) insensitive to CD19-directed chimeric antigen receptor T cells (CAR-T). We hypothesized that TP53 genomic alterations are detrimental to response outcomes in LBCL treated with CD19-CAR-T.

MATERIALS AND METHODS

Patients with LBCL treated with CD19-CAR-T were included. Targeted next-generation sequencing was performed on pre-CAR-T tumor samples in a subset of patients. Response and survival rates by histologic, cytogenetic, and molecular features were assessed. Within a cohort of newly diagnosed LBCL with genomic and transcriptomic profiling, we studied interactions between cellular pathways and TP53 status.

RESULTS

We included 153 adults with relapsed or refractory LBCL treated with CD19-CAR-T (axicabtagene ciloleucel [50%], tisagenlecleucel [32%], and lisocabtagene maraleucel [18%]). Outcomes echoed pivotal trials: complete response (CR) rate 54%, median overall survival (OS) 21.1 months (95% CI, 14.8 to not reached), and progression-free survival 6 months (3.4 to 9.7). Histologic and cytogenetic LBCL features were not predictive of CR. In a subset of 82 patients with next-generation sequencing profiling, CR and OS rates were comparable with the unsequenced cohort. TP53 alterations (mutations and/or copy number alterations) were common (37%) and associated with inferior CR and OS rates in univariable and multivariable regression models; the 1-year OS in TP53-altered LBCL was 44% (95% CI, 29 to 67) versus 76% (65 to 89) in wild-type (P = .012). Transcriptomic profiling from a separate cohort of patients with newly diagnosed lymphoma (n = 562) demonstrated that TP53 alterations are associated with dysregulation of pathways related to CAR-T-cell cytotoxicity, including interferon and death receptor signaling pathway and reduced CD8 T-cell tumor infiltration.

CONCLUSION

TP53 is a potent tumor-intrinsic biomarker that can inform risk stratification and clinical trial design in patients with LBCL treated with CD19-CAR-T. The role of TP53 should be further validated in independent cohorts.

Novel antigen-presenting cell imparts Treg-dependent tolerance to gut microbiota

Establishing and maintaining tolerance to self-antigens or innocuous foreign antigens is vital for the preservation of organismal health. Within the thymus, medullary thymic epithelial cells (mTECs) expressing autoimmune regulator (AIRE) have a critical role in self-tolerance through deletion of autoreactive T cells and promotion of thymic regulatory T (T_reg) cell development^1-4. Within weeks of birth, a separate wave of T_reg cell differentiation occurs in the periphery upon exposure to antigens derived from the diet and commensal microbiota^5-8, yet the cell types responsible for the generation of peripheral T_reg (pT_reg) cells have not been identified. Here we describe the identification of a class of RORγt⁺ antigen-presenting cells called Thetis cells, with transcriptional features of both mTECs and dendritic cells, comprising four major sub-groups (TC I-TC IV). We uncover a developmental wave of Thetis cells within intestinal lymph nodes during a critical window in early life, coinciding with the wave of pT_reg cell differentiation. Whereas TC I and TC III expressed the signature mTEC nuclear factor AIRE, TC IV lacked AIRE expression and was enriched for molecules required for pT_reg generation, including the TGF-β-activating integrin αvβ8. Loss of either major histocompatibility complex class II (MHCII) or ITGB8 by Thetis cells led to a profound impairment in intestinal pT_reg differentiation, with ensuing colitis. By contrast, MHCII expression by RORγt⁺ group 3 innate lymphoid cells (ILC3) and classical dendritic cells was neither sufficient nor required for pT_reg generation, further implicating TC IV as the tolerogenic RORγt⁺ antigen-presenting cell with an essential function in early life. Our studies reveal parallel pathways for the establishment of tolerance to self and foreign antigens in the thymus and periphery, respectively, marked by the involvement of shared cellular and transcriptional programmes.

A phase 2 trial of the somatostatin analog pasireotide to prevent GI toxicity and acute GVHD in allogeneic hematopoietic stem cell transplant

Background

Allogeneic hematopoietic stem cell transplantation (HCT) is an often curative intent treatment, however it is associated with significant gastrointestinal (GI) toxicity and treatment related mortality. Graft-versus-host disease is a significant contributor to transplant-related mortality. We performed a phase 2 trial of the somatostatin analog pasireotide to prevent gastrointestinal toxicity and GVHD after myeloablative allogeneic HCT.

Methods

Patients received 0.9mg pasireotide every 12 hours from the day prior to conditioning through day +4 after HCT (or a maximum of 14 days). The primary outcomes were grade 3–4 gastrointestinal toxicity through day 30 and acute GVHD. Secondary outcomes were chronic GVHD, overall survival and relapse free survival at one year. Stool and blood samples were collected from before and after HCT for analyses of stool microbiome, local inflammatory markers, and systemic inflammatory and metabolic markers. Results were compared with matched controls.

Results

Twenty-six patients received pasireotide and were compared to 52 matched contemporaneous controls using a 1–2 match. Grade 3–4 GI toxicity occurred in 21 (81%) patients who received pasireotide and 35 (67%) controls (p = 0.33). Acute GVHD occurred in 15 (58%) patients in the pasireotide group and 28 (54%) controls (p = 0.94). Chronic GVHD occurred in 16 patients in the pasireotide group (64%) versus 22 patients in the control group (42%) (p = 0.12). Overall survival at 1 year in the pasireotide group was 63% (95% CI: 47%,86%) versus 82% (95% CI: 72%, 93%) in controls (log-rank p = 0.006). Relapse-free survival rate at one year was 40% (95% CI: 25%, 65%) in the pasireotide group versus 78% (95% CI: 68%, 91%) in controls (log-rank p = 0.002). After controlling for the effect of relevant covariates, patients in the pasireotide group had attenuated post-HCT loss of microbial diversity. Analysis of systemic inflammatory markers and metabolomics demonstrated feasibility of such analyses in patients undergoing allogeneic HCT. Baseline level and pre-to-post transplant changes in several inflammatory markers (including MIP1a, MIP1b, TNFa, IL8Pro, and IL6) correlated with likelihood of survival.

Conclusions

Pasireotide did not prevent gastrointestinal toxicity or acute GVHD compared to contemporaneous controls. Pasireotide was associated with numerically higher chronic GVHD and significantly decreased OS and RFS compared to contemporaneous controls. Pasireotide may provide a locally protective effect in the stool microbiome and in local inflammation as measured by stool calprotectin, stool beta-defensin, and stool diversity index.

Abstract IA22: The role of the intestinal microbiome in allogeneic hematopoietic cell transplantation

Relationships between microbiota composition and clinical outcomes of patients following allogeneic hematopoietic cell transplantation (allo-HCT) have been described in single-center studies. Geographic variations in the composition of human microbial communities and differences in clinical practices across institutions raise the question of whether these associations are generalizable. Therefore, we studied 8,767 fecal samples from 1,362 allo-HCT patients at four centers on three continents by 16S ribosomal sequencing. In an observational study, we examined associations between microbiota diversity and overall survival during two years of follow-up after allo-HCT with proportional-hazards analysis. We observed reproducible patterns of microbiota disruption characterized by loss of diversity and domination by single taxa. Low diversity in the peri-neutrophil engraftment period was reproducibly associated with increased risk of death (multivariate-adjusted HR 0.48, 95% CI 0.30-0.77, p = 0.002 in the largest cohort). Subset analysis suggested that these reductions in overall survival were in part due to an increased risk of transplant-related mortality and graft-versus-host disease. Baseline pre-HCT samples already bore evidence of microbiome disruption, and low diversity prior to transplantation was associated with poor survival. In addition, we found that Enterococcus faecium dominates the intestinal microbiota of up to 65% allo-HCT patients early after transplant at all four transplant centers. Enterococcus domination was associated with an increased incidence of acute graft-versus-host disease (GVHD), increased GVHD-related mortality, and reduced overall survival. Post-transplant expansion of Enterococci was also observed in mouse models of GVHD in the absence of antibiotic treatment. Spiking a minimal flora with Enterococci in gnotobiotic mice exacerbated lethal GVHD. Metagenomic sequencing of human and murine Enterococcus-dominated fecal samples revealed an enrichment of lactose and galactose degradation genes, a pathway necessary for Enterococcus growth in vitro. A lactose-free chow attenuated the intestinal outgrowth of Enterococcus and reduced the severity of lethal GVHD in mice. In patients, a lactose-nonabsorber genotype was associated with an increased Enterococcus abundance after cessation of antibiotic treatment after allo-HCT. In conclusion, the concordance of microbiota disruption patterns and their associations with clinical outcomes suggest that approaches to manipulate the intestinal microbiota with the aim of improving allo-HCT clinical outcomes may be generalizable.

Citation Format: Marcel van den Brink. The role of the intestinal microbiome in allogeneic hematopoietic cell transplantation [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr IA22.

Donor and host B7-H4 expression negatively regulates acute graft-versus-host disease lethality

B7-H4 is a negative regulatory B7 family member. We investigated the role of host and donor B7-H4 in regulating acute graft-versus-host disease (GVHD). Allogeneic donor T cells infused into B7-H4-/- versus WT recipients markedly accelerated GVHD-induced lethality. Chimera studies pointed toward B7-H4 expression on host hematopoietic cells as more critical than parenchymal cells in controlling GVHD. Rapid mortality in B7-H4-/- recipients was associated with increased donor T cell expansion, gut T cell homing and loss of intestinal epithelial integrity, increased T effector function (proliferation, proinflammatory cytokines, cytolytic molecules), and reduced apoptosis. Higher metabolic demands of rapidly proliferating donor T cells in B7-H4-/- versus WT recipients required multiple metabolic pathways, increased extracellular acidification rates (ECARs) and oxygen consumption rates (OCRs), and increased expression of fuel substrate transporters. During GVHD, B7-H4 expression was upregulated on allogeneic WT donor T cells. B7-H4-/- donor T cells given to WT recipients increased GVHD mortality and had function and biological properties similar to WT T cells from allogeneic B7-H4-/- recipients. Graft-versus-leukemia responses were intact regardless as to whether B7-H4-/- mice were used as hosts or donors. Taken together, these data provide new insights into the negative regulatory processes that control GVHD and provide support for developing therapeutic strategies directed toward the B7-H4 pathway.

B7-H4 expression in donor T cells and host cells negatively regulates acute graftversus- host disease lethality

The B7 family members are critical in positive and negative regulation of immune responses by engaging various lymphocyte receptors. B7-H4 is a member of the B7 family that can negatively regulate T cell function. We investigated the role of host and donor B7-H4 in regulating acute graft-versus-host disease (GVHD). Allogeneic donor T cells infused into B7-H4−/− versus wild type (WT) recipients markedly accelerated GVHD-induced lethality in a C57BL/6 to BALB/c GVHD model. Chimera studies pointed toward B7-H4 expression on host hematopoietic cells as more critical than parenchymal cells in controlling GVHD. B7-H4−/− recipients had rapid mortality associated with increased donor T cell expansion, gut T cell homing and loss of intestinal epithelial integrity, increased Teffector function (proliferation, pro-inflammatory cytokines, cytolytic molecules) and reduced apoptosis. Higher metabolic demands of rapidly proliferating donor T cells in B7-H4−/− versus WT recipients required multiple metabolic pathways, increased extra-cellular acidification rates and oxygen consumption rates, and increased expression of fuel substrate transporters. Interestingly, during GVHD, B7-H4 expression was upregulated on allogeneic WT donor T cells. Consistent with these data, donor B7-H4−/− T cells given to WT recipients increased GVHD mortality and functioned similarly to WT T cells from allogeneic B7-H4−/− recipients. Graft-versus-leukemia responses were intact regardless as to whether B7-H4−/− mice were used as hosts or donors. Taken together, these data provide new insights into the negative regulatory processes that control GVHD and provide support for developing therapeutic strategies directed toward the B7-H4 pathway.

Genome-Wide Screening for Enteric Colonization Factors in Carbapenem-Resistant ST258 Klebsiella pneumoniae

A diverse, antibiotic-naive microbiota prevents highly antibiotic-resistant microbes, including carbapenem-resistant Klebsiella pneumoniae (CR-Kp), from achieving dense colonization of the intestinal lumen. Antibiotic-mediated destruction of the microbiota leads to expansion of CR-Kp in the gut, markedly increasing the risk of bacteremia in vulnerable patients. While preventing dense colonization represents a rational approach to reduce intra- and interpatient dissemination of CR-Kp, little is known about pathogen-associated factors that enable dense growth and persistence in the intestinal lumen. To identify genetic factors essential for dense colonization of the gut by CR-Kp, we constructed a highly saturated transposon mutant library with >150,000 unique mutations in an ST258 strain of CR-Kp and screened for in vitro growth and in vivo intestinal colonization in antibiotic-treated mice. Stochastic and partially reversible fluctuations in the representation of different mutations during dense colonization revealed the dynamic nature of intestinal microbial populations. We identified genes that are crucial for early and late stages of dense gut colonization and confirmed their role by testing isogenic mutants in in vivo competition assays with wild-type CR-Kp Screening of the transposon library also identified mutations that enhanced in vivo CR-Kp growth. These newly identified colonization factors may provide novel therapeutic opportunities to reduce intestinal colonization by CR-KpIMPORTANCEKlebsiella pneumoniae is a common cause of bloodstream infections in immunocompromised and hospitalized patients, and over the last 2 decades, some strains have acquired resistance to nearly all available antibiotics, including broad-spectrum carbapenems. The U.S. Centers for Disease Control and Prevention has listed carbapenem-resistant K. pneumoniae (CR-Kp) as an urgent public health threat. Dense colonization of the intestine by CR-Kp and other antibiotic-resistant bacteria is associated with an increased risk of bacteremia. Reducing the density of gut colonization by CR-Kp is likely to reduce their transmission from patient to patient in health care facilities as well as systemic infections. How CR-Kp expands and persists in the gut lumen, however, is poorly understood. Herein, we generated a highly saturated mutant library in a multidrug-resistant K. pneumoniae strain and identified genetic factors that are associated with dense gut colonization by K. pneumoniae This study sheds light on host colonization by K. pneumoniae and identifies potential colonization factors that contribute to high-density persistence of K. pneumoniae in the intestine.

Sublethal Total Body Irradiation Causes Long-Term Deficits in Thymus Function by Reducing Lymphoid Progenitors

Total body irradiation (TBI) damages hematopoietic cells in the bone marrow and thymus; however, the long-term effects of irradiation with aging remain unclear. In this study, we found that the impact of radiation on thymopoiesis in mice varied by sex and dose but, overall, thymopoiesis remained suppressed for ≥12 mo after a single exposure. Male and female mice showed a long-term dose-dependent reduction in thymic cKit⁺ lymphoid progenitors that was maintained throughout life. Damage to hematopoietic stem cells (HSCs) in the bone marrow was dose dependent, with as little as 0.5 Gy causing a significant long-term reduction. In addition, the potential for T lineage commitment was radiation sensitive with aging. Overall, the impact of irradiation on the hematopoietic lineage was more severe in females. In contrast, the rate of decline in thymic epithelial cell numbers with age was radiation-sensitive only in males, and other characteristics including Ccl25 transcription were unaffected. Taken together, these data suggest that long-term suppression of thymopoiesis after sublethal irradiation was primarily due to fewer progenitors in the BM combined with reduced potential for T lineage commitment. A single irradiation dose also caused synchronization of thymopoiesis, with a periodic thymocyte differentiation profile persisting for at least 12 mo postirradiation. This study suggests that the number and capability of HSCs for T cell production can be dramatically and permanently damaged after a single relatively low TBI dose, accelerating aging-associated thymic involution. Our findings may impact evaluation and therapeutic intervention of human TBI events.

Role of intestinal microbiota in transplantation outcomes

While allogeneic hematopoietic stem cell transplantations have a curative potential, infections and graft-versus-host disease remain significant problems. The intestinal microbiota can influence responses to cancer chemotherapy and the role of the microbiota in affecting allogeneic hematopoietic stem cell transplantation outcomes is increasingly appreciated. The following paper discusses the most recent developments in this area.

Interleukin-22 directly regulates intestinal stem cell regeneration after tissue damage (MUC8P.722)

Little is known about regulation of the intestinal stem cell (ISC) compartment after injury. We hypothesized that IL-22 could promote intestinal regeneration by either acting on ISCs or by acting on Paneth cells (PCs) making up the ISC niche. Utilizing an in vitro regeneration model, we found that organoids derived from murine small intestine (SI) and large intestine (LI) crypts demonstrated substantially increased size after culture with IL-22. Innate lymphoid cell co-culture also increased organoid size in an IL-22-dependent fashion. IL-22 expanded the Lgr5+ ISC pool within SI organoids, activated STAT3 phosphorylation in Lgr5+ cells, and increased size of organoids cultured from purified SI ISCs. Using a murine allogeneic bone marrow transplant (BMT) model, we found that IL-22 administration led to reduced intestinal graft vs. host disease pathology, increased maintenance of Lgr5+ ISCs, and significantly greater ISC proliferation. ISC protection post-BMT was not due to niche augmentation, as PC numbers, PC-derived growth factors (EGF, Wnt3), and stroma-derived growth factors (R-spondin3) were all unchanged after IL-22 administration. IL-22 receptor (IL-22R) staining further indicated a direct effect of IL-22 on ISCs rather than the niche, as PCs were found to express very little IL-22R and demonstrated no evidence of STAT3 phosphorylation upon in vitro culture. In summary, we found that IL-22 regulates epithelial regeneration after tissue damage by acting directly on ISCs.

Intensified Mycophenolate Mofetil Dosing and Higher Mycophenolic Acid Trough Levels Reduce Severe Acute Graft-versus-Host Disease after Double-Unit Cord Blood Transplantation

Although mycophenolate mofetil (MMF) has replaced corticosteroids as immunosuppression in cord blood transplantation (CBT), optimal MMF dosing has yet to be established. We intensified MMF dosing from every 12 to every 8 hours to augment graft-versus-host disease (GVHD) prophylaxis in double-unit cord blood transplantation (dCBT) and evaluated outcomes according to the total daily MMF dose/kg in 174 dCBT recipients (median age, 39 years; range, 1 to 71) who underwent transplantation for hematologic malignancies. Recipients of an MMF dose ≤ the median (36 mg/kg/day) had an increased day 100 grade III and IV acute GVHD (aGVHD) incidence compared with patients who received >36 mg/kg/day (24% versus 8%, P = .008). Recipients of ≤ the median dose who had highly HLA allele (1 to 3 of 6) mismatched dominant units had the highest day 100 grade III and IV aGVHD incidence of 37% (P = .009). This finding was confirmed in multivariate analysis (P = .053). In 83 patients evaluated for mycophenolic acid (MPA) troughs, those with a mean week 1 and 2 trough < .5 μg/mL had an increased day 100 grade III and IV aGVHD of 26% versus 9% (P = .063), and those who received a low total daily MMF dose and had a low mean week 1 and 2 MPA trough had a 40% incidence (P = .008). Higher MMF dosing or MPA troughs had no impact on engraftment after myeloablation. This analysis supports intensified MMF dosing in milligram per kilogram per day and MPA trough level monitoring early after transplantation in dCBT recipients.

The effects of intestinal tract bacterial diversity on mortality following allogeneic hematopoietic stem cell transplantation

Highly diverse bacterial populations inhabit the gastrointestinal tract and modulate host inflammation and promote immune tolerance. In allogeneic hematopoietic stem cell transplantation (allo-HSCT), the gastrointestinal mucosa is damaged, and colonizing bacteria are impacted, leading to an impaired intestinal microbiota with reduced diversity. We examined the impact of intestinal diversity on subsequent mortality outcomes following transplantation. Fecal specimens were collected from 80 recipients of allo-HSCT at the time of stem cell engraftment. Bacterial 16S rRNA gene sequences were characterized, and microbial diversity was estimated using the inverse Simpson index. Subjects were classified into high, intermediate, and low diversity groups and assessed for differences in outcomes. Mortality outcomes were significantly worse in patients with lower intestinal diversity; overall survival at 3 years was 36%, 60%, and 67% for low, intermediate, and high diversity groups, respectively (P = .019, log-rank test). Low diversity showed a strong effect on mortality after multivariate adjustment for other clinical predictors (transplant related mortality: adjusted hazard ratio, 5.25; P = .014). In conclusion, the diversity of the intestinal microbiota at engraftment is an independent predictor of mortality in allo-HSCT recipients. These results indicate that the intestinal microbiota may be an important factor in the success or failure in allo-HSCT.

Intrathymic innate lymphoid cells: long-lived mediators of immune regeneration (TRAN3P.905)

Innate lymphoid cells (ILC) are a newly described population of immune cells implicated in the maintenance and function of tissues as diverse as liver, gut, lung and lymph nodes. We have recently described a key role for ILC, and their production of IL-22, in endogenous thymic regeneration: a crucial process that allows for renewal of immune competence following immune depletion. Unlike other lymphoid cells, ILC were extremely radio-resistant with little depletion of cells after even lethal doses of total body irradiation. Consistent with these findings, a considerable proportion of ILC were non-cycling in steady-state conditions and expressed high levels of the anti-apoptotic protein Bcl-2. Perhaps unsurprising given their resistance to proliferation-targeted damage, a residual population of host ILC could be identified for up to 12 months after hematopoietic stem cell transplantation and these host ILC were almost exclusively non-proliferating. Intriguingly, although IL-22 appears to play a considerable role in their regenerative capacity, depletion of ILC from IL-22 deficient mice led to significantly worse recovery compared to Il22-/- mice replete with ILC. These pre-clinical studies not only help to identify the mechanisms that allow this nascent cell population to mediate its regenerative effects, but also offer a novel clinical approach to enhance T cell immunity in individuals with deficiencies due to aging, infectious disease, chemotherapy or radiation injury

Early Clostridium difficile infection during allogeneic hematopoietic stem cell transplantation

Clostridium difficile infection (CDI) is frequently diagnosed in recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We characterized early-transplant CDI and its associations, and analyzed serially-collected feces to determine intestinal carriage of toxigenic C. difficile. Fecal specimens were collected longitudinally from 94 patients during allo-HSCT hospitalization, from the start of pre-transplant conditioning until up to 35 days after stem cell infusion. Presence of C. difficile 16S rRNA and tcdB genes was determined. Clinical variables and specimen data were analyzed for association with development of CDI. Historical data from an additional 1144 allo-HSCT patients was also used. Fecal specimens from 37 patients (39%) were found to harbor C. difficile. Early-transplant CDI was diagnosed in 16 of 94 (17%) patients undergoing allo-HSCT; cases were generally mild and resembled non-CDI diarrhea associated with transplant conditioning. CDI was associated with preceding colonization with tcdB-positive C. difficile and conditioning regimen intensity. We found no associations between early-transplant CDI and graft-versus-host disease or CDI later in transplant. CDI occurs with high frequency during the early phase of allo-HSCT, where recipients are pre-colonized with toxigenic C. difficile. During this time, CDI incidence peaks during pre-transplant conditioning, and is correlated to intensity of the treatment. In this unique setting, high rates of CDI may be explained by prior colonization and chemotherapy; however, cases were generally mild and resembled non-infectious diarrhea due to conditioning, raising concerns of misdiagnosis. Further study of this unique population with more discriminating CDI diagnostic tests are warranted.

Donor CD19-targeted T cells exert potent graft versus lymphoma activity without GVHD (P2134)

We evaluated the relative effects of donor CD19-targeting chimeric antigen receptors (CAR)+T cells on the elimination of CD19+B cells and endogenous TCR-mediated GVHD in mouse models of allo-HSCT. We generated a panel of retroviral vectors encoding mouse CD19-specific CARs: CD19-delta, a tail-less CAR lacking the CD3ζ signaling and CD19-CAR signaling through CD28 and CD3ζ. CD19-CAR+T cells mediated specific lysis of CD19+tumors in vitro, while CD19-delta+T cells did not. We next transferred the transduced donor T cells into lethally irradiated recipients of T cell-depleted allografts and CD19+lymphoma A20-TGL (B6→BALB/c+A20-TGL). CD19-CAR+T cells mediated clearance of A20 tumor leading to significantly improved tumor free survival (p&lt;0.01), while mediating significantly less acute GVHD, resulting in improved survival (p&lt;0.001). Donor CD19-delta+T cells caused lethal GVHD, indicating persistent endogenous TCR mediated alloreactivity in the absence of CAR signaling. Compared to controls, fewer alloactivated CD19-CAR+T cells were found in the lymphoid organs of allo-HSCT recipients. This was accompanied by a lower expression of IFN-γ and lower frequencies of phenotypically activated T cells (p&lt;0.05). LPAM, associated with increased gut GVHD, was also significantly lower on CD19-CAR+T cells. CAR stimulation did not inhibit TCR-mediated killing. These results provide the first preclinical evidence suggesting that CAR+ donor T cells may be safely applied in an allogeneic context.

Interleukin-22 drives endogenous thymic regeneration in mice (44.6)

Thymic regeneration is a crucial function that allows for renewal of immune competance after stress, infection or immunodepletion, however the mechanisms governing this rejuvenation remain poorly understood. Here we detail a framework of endogenous thymic regeneration centred on IL-22, a recently identified cytokine primarily implicated in maintenance of epithelial barrier function. Although IL-22 was redundant for steady-state thymopoiesis, thymic recovery was impaired in IL-22-deficient mice and intrathymic levels of IL-22 were significantly increased in WT mice following thymic damage. IL-22, which signalled through thymic epithelial cells and promoted their proliferation and survival, was upregulated by radio-resistant RORγ(t)+NKp46-CCR6+ lymphoid tissue-inducer cells after thymic injury under the control of dendritic cell-derived IL-23 and triggered by the depletion of CD4+CD8+ double positive (DP) thymocytes. Importantly, administration of IL-22 enhanced thymic recovery following irradiation damage. These studies reveal a network of endogenous thymus regeneration where 1) the depletion of DP thymocytes triggers 2) upregulation of IL-23 by DCs that induces 3) the production of IL-22 by thymic LTi. This cascade of events leads to regeneration of the epithelial microenvironment and, ultimately, to rejuvenation of thymopoiesis; presenting an innovative strategy for improving immune competence in patients whose thymus has been damaged from infection or cytoreductive therapy.

IL-22 protects intestinal stem cells from immune-mediated tissue damage and regulates sensitivity to graft vs. host disease (126.31)

Intestinal graft vs. host disease (GVHD) is a major complication of allogeneic bone marrow transplantation (allo-BMT). Strategies to limit GVHD by selective promotion of epithelial regeneration in the absence of immunosuppression are largely unknown. We investigated the role of IL-22 in allo-BMT and found that IL-22 levels in small and large intestine were increased after BMT after radiation injury (RI) without BMT. IL-22 upregulation after RI was dependent on the presence of IL-23p40. Although intestinal IL-22 levels were increased after T cell-depleted (TCD) BMT, intestinal IL-22 was reduced by GVHD, as IL-22 production was mediated by host-derived innate lymphoid cells (ILC) that were eliminated by GVHD. Furthermore, host-derived IL-22 was critical for reduction of GVHD morbidity, mortality, and intestinal pathology. GVHD in IL-22 KO mice led to increased apoptosis in epithelial crypts where the intestinal epithelial stem/progenitor cell niche is located. Immunohistochemistry and immunofluorescence demonstrated IL-22 receptor expression on intestinal stem cells (ISC) and progenitors. Allo-BMT in Lgr5-LacZ reporter mice indicated that ISC were targeted by GVHD, and GVHD in IL-22 KO mice led to dramatic ISC depletion. IL-22 is thus critical for protection of host epithelium during GVHD and critical for protection of ISC. These findings may have broad relevance for protection of ISC and intestinal epithelium in clinical GVHD and other inflammatory intestinal diseases.

Janus kinase 2 offers a precise therapeutic target against DC stimulated alloreactivity in transplantation (169.21)

JAK2 is critical to cytokine signaling and has a specific role in mediating alloreactivity. We have demonstrated that specific JAK2 inhibition with TG101348 suppresses alloimmunity stimulated by human dendritic cells in vitro, while maintaining immunity against viral antigens. JAK2 inhibition also extends survival in a mouse graft-versus-host disease (GvHD) model. Methods: Major MHC-mismatch models were used in human and mouse experiments. Human moDC and moDC:T cell cultures were treated with either TG101348 (1uM) or vehicle. Mice underwent 850 cGy irradiation followed by T cell-depleted marrow and splenic T cells. TG101348 (60mg/kg) or vehicle was administered per oral gavage daily. Results: JAK2 inhibition reduced the expression of CD83 and CCR7 in 2-day cytokine-matured moDCs (p&lt;0.05) and suppressed T cell proliferation in a 5-day alloMLR (p&lt;0.005). JAK2 blockade preserved allogeneic Tregs (p=NS), and enhanced the Treg:CD8+CD25+ T cell ratio (p&lt;0.05). T cells exposed to JAK2-inhibited DCs maintained tolerance to alloantigen restimulation, with preserved response to flu-loaded autologous moDCs. JAK2 inhibition delayed the onset of GvHD and improved survival in BALB/c mice that received B6 marrow and T cells (median survival JAK2 inhibitor 35 days vs vehicle 25 days, p&lt;0.005). All mice engrafted. Conclusions: JAK2 offers a novel, specific therapeutic target against GvHD and allograft rejection by suppressing DC allostimulation of T cells, without broader immune impairment.

Transplantation in remission improves the disease-free survival of patients with advanced myelodysplastic syndromes treated with myeloablative T cell-depleted stem cell transplants from HLA-identical siblings

From 1985 to 2004, 49 patients with advanced myelodysplastic syndromes (MDS) (> or =5% blasts) or acute myeloid leukemia (AML) transformed from MDS underwent T cell depleted bone marrow or peripheral blood hematopoietic stem cell transplantation (HSCT) from HLA-identical siblings following conditioning with a myeloablative regimen that included total body irradiation (44 patients) or busulfan (5 patients). Thirty-six patients received chemotherapy (3 low dose and 33 induction doses) before conditioning, and 13 patients did not receive any chemotherapy. Prior to transplantation, 22 of the 36 treated patients were in hematologic remission; 4 were in a second refractory cytopenia phase (26 responders); 8 had failed to achieve remission; and 2 of the responders had progression or relapse of their MDS (10 failures). No post-transplantation pharmacologic prophylaxis for graft-versus-host disease (GVHD) was given. The median age was 48 yrs (range 13-61). Forty-five of the 49 patients engrafted; 2 had primary graft failure; and 2 died before engraftment. Only 3 patients developed acute GVHD (aGVHD) (grades I and III) and 1 chronic GVHD (cGVHD). At 3 yrs post-transplantation, the overall survival (OS) was 54% in the responders; 31% in the untreated group; and 0% in the failure group (P=.0004). The disease free survival (DFS) was 50%, 15% and 0% in each group respectively (P=.0008). In multivariate analysis, disease status before cytoreduction remained highly correlated with DFS (P<.001). The cumulative incidence (CI) of relapse at 2-yrs post-transplantation for the responders was 23%; for the untreated group was 38%; and for the failures was 50%. The CI of non-relapse mortality at 2-yrs post-transplantation, for the responders was 23%; for the untreated group was 38%; and for the failures was 40%. All survivors achieved a Karnofsky Performance Status (KPS) of > or =90. These results indicate that patients with advanced MDS who achieve and remain in remission or a second refractory cytopenia phase with chemotherapy before conditioning can achieve successful long-term remissions following a myeloablative T cell depleted allogeneic HSCT.

Preparing for the unthinkable: emergency preparedness for the hematopoietic cell transplant program

Emergencies come at the most inopportune times. Some are totally unexpected, others come with short warnings. Although rare, an emergency comes with the potential to wreak disaster and pose serious risk to the services provided to hematopoietic cell transplant (HCT) patients. Yet, the consequences of an emergency can be mitigated by thinking the unthinkable and having a plan for emergency preparedness in place. Each HCT center should develop a plan containing steps of mitigation, preparedness, response and recovery. This report provides the framework for a HCT-specific emergency preparedness plan that can be used by individual centers to develop customized guidelines on preparing for, responding to, and recovering from an emergency.

Molecular imaging reveals skeletal engraftment sites of transplanted bone marrow cells

Molecular imaging holds great promise for the in vivo study of cell therapy. Our hypothesis was that multimodality molecular imaging can identify the initial skeletal engraftment sites post-bone marrow cell transplantation. Utilizing a standard mouse model of bone marrow (BM) transplantation, we introduced a combined bioluminescence (BLI) and positron emission tomography (PET) imaging reporter gene into mouse bone marrow cells. Bioluminescence imaging was used for monitoring serially the early in vivo BM cell engraftment/expansion every 24 h. Significant cell engraftment/expansion was noted by greatly increased bioluminescence about 1 week posttransplant. Then PET was applied to acquire three-dimensional images of the whole-body in vivo biodistribution of the transplanted cells. To localize cells in the skeleton, PET was followed by computed tomography (CT). Co-registration of PET and CT mapped the sites of BM engraftment. Multiple, discrete BM cell engraftment sites were observed. Taken together, this multimodality approach may be useful for further in vivo characterization of various therapeutic cell types.