Dynamics of Expression of Programmed Cell Death Protein-1 (PD-1) on T Cells After Allogeneic Hematopoietic Stem Cell Transplantation

Remission of relapsed/refractory classical Hodgkin lymphoma induced by brentuximab vedotin and pembrolizumab combination after allogeneic hematopoietic stem cell transplantation: a case report

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment option for patients with highly chemorefractory Hodgkin lymphoma (HL). The CD30-targeting antibody-drug conjugate Brentuximab-Vedotin (BV) and programmed cell death protein-1 (PD-1) blocking agents have demonstrated clinical activity with durable responses in relapsed/refractory (r/r) HL. However, patients with a history of allo-HSCT were frequently excluded from clinical trials due to concerns about the risk of graft-versus-host disease (GVHD). We report the clinical history of a patient with refractory classical HL who underwent two allo-HSCTs (first from matched unrelated and second from haploidentical donor) after relapsing on BV and nivolumab and for whom durable remission was finally obtained using BV-pembrolizumab combination for relapse after haploidentical HSCT. Such treatment was associated with the onset of GVHD after only two cycles which led to treatment discontinuation. However, the side effects were rapidly controlled, and after 2 years of follow-up, the patient is still in remission. Our data support the feasibility and efficacy of combining PD-1 blockade with BV to enhance the graft-versus-lymphoma effect after allo-HSCT.

hPMSCs Regulate the Level of TNF-α and IL-10 in Th1 Cells and Improve Hepatic Injury in a GVHD Mouse Model via CD73/ADO/Fyn/Nrf2 Axis

Mesenchymal stem cells (MSCs) ameliorate graft-versus-host disease (GVHD)-induced tissue damage by exerting immunosuppressive effects. However, the related mechanism remains unclear. Here, we explored the therapeutic effect and mechanism of action of human placental-derived MSCs (hPMSCs) on GVHD-induced mouse liver tissue damage, which shows association with inflammatory responses, fibrosis accompanied by hepatocyte tight junction protein loss, the upregulation of Bax, and the downregulation of Bcl-2. It was observed in GVHD mice and Th1 cell differentiation system that hPMSCs treatment increased IL-10 levels and decreased TNF-α levels in the Th1 subsets via CD73. Moreover, hPMSCs treatment reduced tight junction proteins loss and inhibited hepatocyte apoptosis in the livers of GVHD mice via CD73. ADO level analysis in GVHD mice and the Th1 cell differentiation system showed that hPMSCs could also upregulate ADO levels via CD73. Moreover, hPMSCs enhanced Nrf2 expression and diminished Fyn expression via the CD73/ADO pathway in Th1, TNF-α+, and IL-10+ cells. These results indicated that hPMSCs promoted and inhibited the secretion of IL-10 and TNF-α, respectively, during Th1 cell differentiation through the CD73/ADO/Fyn/Nrf2 axis signaling pathway, thereby alleviating liver tissue injury in GVHD mice.

Reduced mitochondrial respiration in peripheral T cells after paediatric heamatopoietic stem cell transplantation

Background

Recovery and functional differentiation of T-cell subsets are central for the development of immune function and complications after allogeneic hematopoietic stem cell transplantation (HSCT), but little is known about the cellular respiration and factors influencing T-cell metabolic fitness during immune maturation after HSCT.

Method

We included 20 HSCT patients and analysed mitochondrial oxidative phosphorylation and mitochondrial fitness in peripheral blood mononuclear cell samples collected at days +90 and +180 after HSCT.

Results

Phenotypic analysis revealed lower overall T-cell counts, lower CD4+/CD8+ ratio and a skewed distribution of early T-cell subsets at day +90, gradually recovering by day +180. Although ATP turnover in HSCT patients was similar to healthy controls, the spare respiratory capacity (SRC) of T cells, reflecting the available energy reserve, was significantly reduced at day +90 and +180 compared to healthy controls. This reduction in SRC was not correlated with the occurrence of acute graft-versus-host disease (aGVHD), the intensity of conditioning regimens and markers of T-cell exhaustion.

Conclusion

We found significantly depressed SRC until six months post-HSCT, but we were not able to identify transplant-related risk factors or associations with the clinical outcome.

Phase II trial of hypomethylating agent combined with nivolumab for acute myeloid leukaemia relapse after allogeneic haematopoietic cell transplantation-Immune signature correlates with response

Acute myeloid leukaemia (AML) relapse after allogeneic haematopoietic cell transplantation (allo-HCT) is often driven by immune-related mechanisms and associated with poor prognosis. Immune checkpoint inhibitors combined with hypomethylating agents (HMA) may restore or enhance the graft-versus-leukaemia effect. Still, data about using this combination regimen after allo-HCT are limited. We conducted a prospective, phase II, open-label, single-arm study in which we treated patients with haematological AML relapse after allo-HCT with HMA plus the anti-PD-1 antibody nivolumab. The response was correlated with DNA-, RNA- and protein-based single-cell technology assessments to identify biomarkers associated with therapeutic efficacy. Sixteen patients received a median number of 2 (range 1-7) nivolumab applications. The overall response rate (CR/PR) at day 42 was 25%, and another 25% of the patients achieved stable disease. The median overall survival was 15.6 months. High-parametric cytometry documented a higher frequency of activated (ICOS+ , HLA-DR+ ), low senescence (KLRG1- , CD57- ) CD8+ effector T cells in responders. We confirmed these findings in a preclinical model. Single-cell transcriptomics revealed a pro-inflammatory rewiring of the expression profile of T and myeloid cells in responders. In summary, the study indicates that the post-allo-HCT HMA/nivolumab combination induces anti-AML immune responses in selected patients and could be considered as a bridging approach to a second allo-HCT. Trial-registration: EudraCT-No. 2017-002194-18.

The Synergistic Potential of Combining PD-1/PD-L1 Immune Checkpoint Inhibitors with NOD2 Agonists in Alzheimer's Disease Treatment

Our research over the past decade has compellingly demonstrated the potential of Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) receptor agonists in Alzheimer's disease (AD) treatment. These agonists facilitate the conversation of pro-inflammatory monocytes into patrolling monocytes, leading to the efficient clearance of amyloid-β (Aβ) in the AD-affected cerebrovascular system. This approach surpasses the efficacy of targeting Aβ formation, marking a significant shift in therapeutic strategies. Simultaneously, inhibitors of PD-1/PD-L1 immune check point or glycogen synthase kinase 3 beta (GSK3β), which modulates PD-1, have emerged as potent AD treatment modalities. PD-1 inhibitor exhibits a profound potential in monocytes' recruitment to the AD-afflicted brain. Recent evidence suggests that an integrated approach, combining the modulation of NOD2 and PD-1, could yield superior outcomes. This innovative combinatorial therapeutic approach leverages the potential of MDP to act as a catalyst for the conversion of inflammatory monocytes into patrolling monocytes, with the subsequent recruitment of these patrolling monocytes into the brain being stimulated by the PD-1 inhibitor. These therapeutic interventions are currently under preclinical investigation by pharmaceutical entities, underscoring the promise they hold. This research advocates for the modulation, rather than suppression, of the innate immune system as a promising pharmacological strategy in AD.

Galectin-3 expression in donor T cells reduces GvHD severity and lethality after allogeneic hematopoietic cell transplantation

Abundant donor cytotoxic T cells that attack normal host organs remain a major problem for patients receiving allogeneic hematopoietic cell transplantation (allo-HCT). Despite an increase in our knowledge of the pathobiology of acute graft versus host disease (aGvHD), the mechanisms regulating the proliferation and function of donor T cells remain unclear. Here, we show that activated donor T cells express galectin-3 (Gal-3) after allo-HCT. In both major and minor histocompatibility-mismatched models of murine aGvHD, expression of Gal-3 is associated with decreased T cell activation and suppression of the secretion of effector cytokines, including IFN-γ and GM-CSF. Mechanistically, Gal-3 results in activation of NFAT signaling, which can induce T cell exhaustion. Gal-3 overexpression in human T cells prevents severe disease by suppressing cytotoxic T cells in xenogeneic aGvHD models. Together, these data identify the Gal-3-dependent regulatory pathway in donor T cells as a critical component of inflammation in aGvHD.

Exploring the Bio-Functional Effect of Single Nucleotide Polymorphisms in the Promoter Region of the TNFSF4, CD28, and PDCD1 Genes

In a prior study, we discovered that hematopoietic stem cell transplantation (HSCT) and/or autoimmune diseases, such as systemic lupus erythematosus, were associated with the rs1234314 C/G and rs45454293 C/T polymorphisms of TNFSF4, the rs5839828 C > del and rs36084323 C > T polymorphisms of PDCD1, and the rs28541784C/T, rs200353921A/T, rs3181096C/T, and rs3181098 G/A polymorphisms of CD28. However, the association does not imply causation. These single nucleotide polymorphisms (SNPs) are all located in the promoter region of these genes, so we used the dual-luminescence reporter assay to explore the effect of single nucleotide polymorphisms (SNPs) on transcriptional activity. For each promoter–reporter with a single SNP mutation, more than 10 independent experiments were carried out, and the difference in transcription activity was compared using one-way ANOVA and Tukey’s honestly significant difference test. The results showed that the G-allele of rs1234314 had 0.32 ± 0.09 times the average amount of relative light units (RLU) compared to the C-allele (p = 0.003), the T-allele of rs45454293 had 4.63 ± 0.92 times the average amount of RLU compared to the C-allele (p < 0.001), the del-allele of rs5839828 had 1.37 ± 0.24 times the average amount of RLU compared to the G-allele (p < 0.001), and the T-allele of rs36084323 had 0.68 ± 0.07 times the average amount of RLU compared to the C-allele (p < 0.001). The CD28 SNPs studied here did not affect transcriptional activity. In conclusion, the findings of this study could only confirm that the SNP had a bio-functional effect on gene expression levels. According to the findings, several SNPs in the same gene have bio-functions that affect transcriptional activity. However, some increase transcriptional activity while others decrease it. Consequently, we inferred that the final protein level should be the integration result of the co-regulation of all the SNPs with the effect on transcriptional activity.

Aberrant T-cell exhaustion in severe combined immunodeficiency survivors with poor T-cell reconstitution after transplantation

BACKGROUND

Severe combined immunodeficiency (SCID) comprises rare inherited disorders of immunity that require definitive treatment through hematopoietic cell transplantation (HCT) or gene therapy for survival. Despite successes of allogeneic HCT, many SCID patients experience incomplete immune reconstitution, persistent T-cell lymphopenia, and poor long-term outcomes.

OBJECTIVE

We hypothesized that CD4+ T-cell lymphopenia could be associated with a state of T-cell exhaustion in previously transplanted SCID patients.

METHODS

We analyzed markers of exhaustion in blood samples from 61 SCID patients at a median of 10.4 years after HCT.

RESULTS

Compared to post-HCT SCID patients with normal CD4+ T-cell counts, those with poor T-cell reconstitution showed lower frequency of naive CD45RA+/CCR7+ T cells, recent thymic emigrants, and TCR excision circles. They also had a restricted TCR repertoire, increased expression of inhibitory receptors (PD-1, 2B4, CD160, BTLA, CTLA-4), and increased activation markers (HLA-DR, perforin) on their total and naive CD8+ T cells, suggesting T-cell exhaustion and aberrant activation, respectively. The exhaustion score of CD8+ T cells was inversely correlated with CD4+ T-cell count, recent thymic emigrants, TCR excision circles, and TCR diversity. Exhaustion scores were higher among recipients of unconditioned HCT, especially when further in time from HCT. Patients with fewer CD4+ T cells showed a transcriptional signature of exhaustion.

CONCLUSIONS

Recipients of unconditioned HCT for SCID may develop late post-HCT T-cell exhaustion as a result of diminished production of T-lineage cells. Elevated expression of inhibitory receptors on their T cells may be a biomarker of poor long-term T-cell reconstitution.

Depletion of exhausted alloreactive T cells enables targeting of stem-like memory T cells to generate tumor-specific immunity

Some hematological malignancies such as multiple myeloma are inherently resistant to immune-mediated antitumor responses, the cause of which remains unknown. Allogeneic bone marrow transplantation (alloBMT) is the only curative immunotherapy for hematological malignancies due to profound graft-versus-tumor (GVT) effects, but relapse remains the major cause of death. We developed murine models of alloBMT where the hematological malignancy is either sensitive [acute myeloid leukemia (AML)] or resistant (myeloma) to GVT effects. We found that CD8+ T cell exhaustion in bone marrow was primarily alloantigen-driven, with expression of inhibitory ligands present on myeloma but not AML. Because of this tumor-independent exhaustion signature, immune checkpoint inhibition (ICI) in myeloma exacerbated graft-versus-host disease (GVHD) without promoting GVT effects. Administration of post-transplant cyclophosphamide (PT-Cy) depleted donor T cells with an exhausted phenotype and spared T cells displaying a stem-like memory phenotype with chromatin accessibility present in cytokine signaling genes, including the interleukin-18 (IL-18) receptor. Whereas ICI with anti-PD-1 or anti-TIM-3 remained ineffective after PT-Cy, administration of a decoy-resistant IL-18 (DR-18) strongly enhanced GVT effects in both myeloma and leukemia models, without exacerbation of GVHD. We thus defined mechanisms of resistance to T cell-mediated antitumor effects after alloBMT and described an immunotherapy approach targeting stem-like memory T cells to enhance antitumor immunity.

PD-1 suppresses the osteogenic and odontogenic differentiation of stem cells from dental apical papilla via targeting SHP2/NF-κB axis

Stem cells from the apical papilla (SCAPs) are important for tooth root development and regeneration of root dentin. Here, we examined the expression of programmed cell death protein-1 (PD-1) in SCAPs and investigated the effect of PD-1 on odontogenic and osteogenic differentiation and the relationship between PD-1 and SHP2/NF-κB signals. SCAPs were obtained and cultured in the related medium. The proliferation ability was evaluated by cell counting kit 8 (CCK-8) and 5-ethynyl-20-deoxyuridine (EdU) assay. Alkaline phosphatase (ALP) activity assay, ALP staining, western blot, real time quantitative reverse-transcription polymerase chain reaction (RT-qPCR), Alizarin Red S (ARS) staining, and immunofluorescence (IF) staining were performed to explore the osteo/odontogenic potential and the involvement of SHP2/NF-κB pathways. Besides, we transplanted SCAPs component into mouse calvaria defects to evaluate osteogenesis in vivo. We found that human SCAPs expressed PD-1 for the first time. PD-1 knockdown enhanced the osteo/odontogenic differentiation of SCAPs by suppressing SHP2 pathway and activating NF-κB pathway. Overexpression of PD-1 inhibited the osteogenesis and odontogenesis of SCAPs via activation of SHP2 signal and inhibition of NF-κB pathway. PD-1 activated SHP2 signal to block NF-κB signal and then played a vital role in osteo/odontogenic differentiation of SCAPs.

Immune cell subsets in interface cutaneous immune-related adverse events (cirAEs) associated with anti-PD-1 therapy resemble acute graft vs host disease more than lichen planus

Background

Checkpoint immunotherapy is frequently associated with cutaneous immune‐related adverse events (cirAEs), and among those, the most common subtype shows interface reaction patterns that have been likened to lichen planus (LP); however, cutaneous acute graft versus host disease (aGVHD) may be a closer histopathologic comparator. We used quantitative pathology to compare the immunologic composition of anti‐PD‐1‐associated interface reactions to LP and aGVHD to assess for similarities and differences between these cutaneous eruptions.

Methods

Immunohistochemistry for CD4, CD8, CD68, PD‐1, and PD‐L1 was performed on formalin‐fixed paraffin‐embedded tissue from patients with anti‐PD‐1 interface cirAEs (n = 4), LP (n = 9), or aGVHD (n = 5). Densities of immune cell subsets expressing each marker were quantified using the HALO image analysis immune cell module. Plasma cell and eosinophil density were quantified on routine H&E slides.

Results

Specimens from patients with anti‐PD‐1 interface cirAEs showed equivalent total cell densities and immune cell composition to those with aGVHD. Patients with LP showed higher total immune cell infiltration, higher absolute T‐cell densities, increased CD8 proportion, and reduced histiocytic component. The cases with the highest plasma cell counts were all anti‐PD‐1 interface cirAEs and aGVHD.

Conclusion

The composition of immune cell subsets in anti‐PD‐1 interface cirAEs more closely resembles the immune response seen in aGVHD than LP within our cohort. This warrants a closer look via advanced analytics and may have implications for shared pathogenesis and potential treatment options.

Case Report: Preemptive Treatment With Low-Dose PD-1 Blockade and Azacitidine for Molecular Relapsed Acute Myeloid Leukemia With RUNX1-RUNX1T1 After Allogeneic Hematopoietic Stem Cell Transplantation

Acute myeloid leukemia (AML) patients who develop hematological relapse (HR) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) generally have dismal clinical outcomes. Measurable residual disease (MRD)-directed preemptive interventions are effective approaches to prevent disease progression and improve prognosis for molecular relapsed patients with warning signs of impending HR. In this situation, boosting the graft-vs-leukemia (GVL) effect with immune checkpoint inhibitors (ICIs) might be a promising prevention strategy, despite the potential for causing severe graft-vs-host disease (GVHD). In the present study, we reported for the first time an AML patient with RUNX1-RUNX1T1 who underwent preemptive treatment with the combined application of tislelizumab (an anti-PD-1 antibody) and azacitidine to avoid HR following allo-HSCT. On day +81, molecular relapse with MRD depicted by RUNX1-RUN1T1-positivity as well as mixed donor chimerism occurred in the patient. On day +95, with no signs of GVHD and an excellent eastern cooperative oncology group performance status (ECOG PS), the patient thus was administered with 100 mg of tislelizumab on day 1 and 100 mg of azacitidine on days 1-7. After the combination therapy, complete remission was successfully achieved with significant improvement in hematologic response, and the MRD marker RUNX1-RUNX1T1 turned negative, along with a complete donor chimerism in bone marrow. Meanwhile, the patient experienced moderate GVHD and immune-related adverse events (irAEs), successively involving the lung, liver, lower digestive tract and urinary system, which were well controlled by immunosuppressive therapies. As far as we know, this case is the first one to report the use of tislelizumab in combination with azacitidine to prevent post-transplant relapse in AML. In summary, the application of ICIs in MRD positive patients might be an attractive strategy for immune modulation in the future to reduce the incidence of HR in the post-transplant setting, but safer clinical application schedules need to be explored.

CD4 T-Cell Exhaustion: Does It Exist and What Are Its Roles in Cancer?

In chronic infections and in cancer, persistent antigen stimulation under suboptimal conditions can lead to the induction of T-cell exhaustion. Exhausted T cells are characterized by an increased expression of inhibitory markers and a progressive and hierarchical loss of function. Although cancer-induced exhaustion in CD8 T cells has been well-characterized and identified as a therapeutic target (i.e., via checkpoint inhibition), in-depth analyses of exhaustion in other immune cell types, including CD4 T cells, is wanting. While perhaps attributable to the contextual discovery of exhaustion amidst chronic viral infection, the lack of thorough inquiry into CD4 T-cell exhaustion is particularly surprising given their important role in orchestrating immune responses through T-helper and direct cytotoxic functions. Current work suggests that CD4 T-cell exhaustion may indeed be prevalent, and as CD4 T cells have been implicated in various disease pathologies, such exhaustion is likely to be clinically relevant. Defining phenotypic exhaustion in the various CD4 T-cell subsets and how it influences immune responses and disease severity will be crucial to understanding collective immune dysfunction in a variety of pathologies. In this review, we will discuss mechanistic and clinical evidence for CD4 T-cell exhaustion in cancer. Further insight into the derivation and manifestation of exhaustive processes in CD4 T cells could reveal novel therapeutic targets to abrogate CD4 T-cell exhaustion in cancer and induce a robust antitumor immune response.

Low Soluble Programmed Cell Death Protein 1 Levels After Allogeneic Stem Cell Transplantation Predict Moderate or Severe Chronic GvHD and Inferior Overall Survival

Programmed cell death protein-1 (PD-1) is an inhibitory co-receptor required for regulating immune responsiveness and maintaining immune homeostasis. As PD-1 can be released as bioactive soluble molecule, we investigated the clinical significance of soluble PD-1 (sPD-1) after allogeneic hematopoietic stem cell transplantation (HSCT) regarding graft-versus-host disease (GvHD), relapse, and overall survival (OS) in a mono-centric cohort of 82 patients. Compared to pre-HSCT and to healthy controls, post-HSCT sPD-1 plasma levels were significantly increased during an observation time of three months. Univariate analysis revealed that low sPD-1 plasma levels at month one, two or three post HSCT were associated with acute GvHD grade III-IV, the onset of moderate/severe chronic GvHD (cGvHD) and inferior OS, DFS, and TRM, respectively. No relationship was detected to relapse rates. sPD-1 plasma levels were significantly increased in ATG-treated patients compared to ATG-untreated patients. Multivariate analysis revealed that a low sPD-1 plasma levels status at one or two month(s) after HSCT is an independent indicator for inferior OS, DFS, or TRM. A low sPD-1 plasma levels status at month three post HSCT is predictive for the onset of moderate/severe cGvHD. Thus, our study pinpoints the soluble inhibitory co-receptor PD-1 as a promising candidate molecule for the prediction of clinical HSCT outcome.

Immune Checkpoint Programmed Cell Death Protein-1 (PD-1) Expression on Bone Marrow T Cell Subsets in Patients With Plasma Cell Myeloma

Background

Plasma cell myeloma (PCM) is caused by immune dysregulation. We evaluated the expression of immune checkpoint programmed cell death protein-1 (PD-1) on T cell subsets in PCM patients according to disease course and cytogenetic abnormalities. This study aimed to find a target group suitable for therapeutic use of PD-1 blockade in PCM.

Methods

A total of 188 bone marrow (BM) samples from 166 PCM patients and 32 controls were prospectively collected between May 2016 and May 2017. PD-1 expression on BM T cell subsets was measured using flow cytometry.

Results

At diagnosis, the median PD-1 expression on CD4⁺ T cells was 24.6%, which did not significantly differ from that in controls. After stem cell transplantation, PD-1 expression on CD4⁺ T cells was higher than that at diagnosis (P<0.001), regardless of residual disease. PD-1 expression on CD4⁺ T cells in patients with residual disease after chemotherapy was significantly higher than that at diagnosis (P=0.001) and after complete remission following chemotherapy (P=0.044). PD-1 expression on CD8⁺ T cells was higher in PCM patients with cytogenetic abnormalities, including monosomy 13, 1q gain, complex karyotype, and hypodiploidy.

Conclusions

PD-1 blockade might have therapeutic potential in refractory PCM patients after chemotherapy, especially in those with high- or intermediate-risk cytogenetic abnormalities.

Tissue-resident PSGL1loCD4+ T cells promote B cell differentiation and chronic graft-versus-host disease-associated autoimmunity

CD4+ T cell interactions with B cells play a critical role in the pathogenesis of systemic autoimmune diseases such as systemic lupus and chronic graft-versus-host disease (cGVHD). Extrafollicular CD44hiCD62LloPSGL1loCD4+ T cells (PSGL1loCD4+ T cells) are associated with the pathogenesis of lupus and cGVHD, but their causal role has not been established. With murine and humanized MHC-/-HLA-A2+DR4+ murine models of cGVHD, we showed that murine and human PSGL1loCD4+ T cells from GVHD target tissues have features of B cell helpers with upregulated expression of programmed cell death protein 1 (PD1) and inducible T cell costimulator (ICOS) and production of IL-21. They reside in nonlymphoid tissues without circulating in the blood and have features of tissue-resident memory T cells with upregulated expression of CD69. Murine PSGL1loCD4+ T cells from GVHD target tissues augmented B cell differentiation into plasma cells and production of autoantibodies via their PD1 interaction with PD-L2 on B cells. Human PSGL1loCD4+ T cells were apposed with memory B cells in the liver tissues of humanized mice and cGVHD patients. Human PSGL1loCD4+ T cells from humanized GVHD target tissues also augmented autologous memory B cell differentiation into plasma cells and antibody production in a PD1/PD-L2-dependent manner. Further preclinical studies targeting tissue-resident T cells to treat antibody-mediated features of autoimmune diseases are warranted.

Highly proliferative and functional PD-1+ and TIM-3+ T cells are transiently increased in multiple myeloma following autologous hematopoietic stem cell transplantation

The aim of our prospective study was to assess recovery dynamics and functional characteristics of PD-1⁺ and TIM-3⁺ T cells in multiple myeloma (MM) patients following high-dose chemotherapy (HDCT) with autologous hematopoietic stem cell transplantation (AHSCT). Peripheral blood, autograft and bone marrow samples were obtained from 46 MM patients before conditioning, at the engraftment, following six and 12 months post-transplant. Frequencies of CD4⁺ and CD8⁺ T cells expressing PD-1 and TIM-3 and intracellular expression of Ki-67 and Granzyme B were evaluated. Counts of PD-1⁺ and TIM-3⁺ T cells at the engraftment were significantly higher comparing with the levels before HDCT and 6-12 months following AHSCT. The post-transplant increase in the studied subsets was due to a temporary enhancement in proliferation activity. The cytotoxic potential of PD-1- and TIM-3-expressing CD8⁺ T cells was higher at the engraftment comparing with the pre-transplant and remained at the same level for at least 12 months. The increase in CD4⁺PD-1⁺ and CD8⁺TIM-3⁺ T cells at the engraftment was associated with higher absolute counts of their reinfused counterparts. Circulating PD-1⁺ CD8⁺ and TIM-3⁺ CD4⁺ T cells were increased in patients after post-transplant relapse comparing with the ones in remission. Homeostatic proliferation plays a key role in the upregulation of inhibitory checkpoint receptors on functional T cells under lymphopenic conditions. In this regard, it is difficult to predict both the efficacy and adverse reactions of therapy with checkpoint inhibitors on the course of MM after HDCT with AHSCT. Précis. Homeostatic proliferation plays apparently a key role in the upregulation of PD-1 and TIM-3 on functional T cells after AHSCT and appears to be a normal physiological process, contrary to relapse-associated increase in PD-1⁺ and TIM-3⁺ T cells.

Deregulated Expression of Immune Checkpoints on Circulating CD4 T Cells May Complicate Clinical Outcome and Response to Treatment with Checkpoint Inhibitors in Multiple Myeloma Patients

Unlike solid-tumor patients, a disappointingly small subset of multiple myeloma (MM) patients treated with checkpoint inhibitors derive clinical benefits, suggesting differential participation of inhibitory receptors involved in the development of T-cell-mediated immunosuppression. In fact, T cells in MM patients have recently been shown to display features of immunosenescence and exhaustion involved in immune response inhibition. Therefore, we aimed to identify the dominant inhibitory pathway in MM patients to achieve its effective control by therapeutic interventions. By flow cytometry, we examined peripheral blood (PB) CD4 T cell characteristics assigned to senescence or exhaustion, considering PD-1, CTLA-4, and BTLA checkpoint expression, as well as secretory effector function, i.e., capacity for IFN-γ and IL-17 secretion. Analyses were performed in a total of 40 active myeloma patients (newly diagnosed and treated) and 20 healthy controls. At the single-cell level, we found a loss of studied checkpoints’ expression on MM CD4 T cells (both effector (Teff) and regulatory (Treg) cells) primarily at diagnosis; the checkpoint deficit in MM relapse was not significant. Nonetheless, PD-1 was the only checkpoint distributed on an increased proportion of T cells in all MM patients irrespective of disease phase, and its expression on CD4 Teff cells correlated with adverse clinical courses. Among patients, the relative defect in secretory effector function of CD4 T cells was more pronounced at myeloma relapse (as seen in declined Th1/Treg and Th17/Treg cell rates). Although the contribution of PD-1 to MM clinical outcomes is suggestive, our study clearly indicated that the inappropriate expression of immune checkpoints (associated with dysfunctionality of CD4 T cells and disease clinical phase) might be responsible for the sub-optimal clinical response to therapeutic checkpoint inhibitors in MM.

Post-transplantation cyclophosphamide reduces the incidence of acute graft-versus-host disease in patients with acute myeloid leukemia/myelodysplastic syndromes who receive immune checkpoint inhibitors after allogeneic hematopoietic stem cell transplantation

Background

Immune checkpoint inhibitors (ICIs) are being used after allogeneic hematopoietic stem cell transplantation (alloHCT) to reverse immune dysfunction. However, a major concern for the use of ICIs after alloHCT is the increased risk of graft-versus-host disease (GVHD). We analyzed the association between GVHD prophylaxis and frequency of GVHD in patients who had received ICI therapy after alloHCT.

Methods

A retrospective study was performed in 21 patients with acute myeloid leukemia (n=16) or myelodysplastic syndromes (n=5) who were treated with antiprogrammed cell death protein 1 (16 patients) or anticytotoxic T lymphocyte-associated antigen 4 (5 patients) therapy for disease relapse after alloHCT. Associations between the type of GVHD prophylaxis and incidence of GVHD were analyzed.

Results

Four patients (19%) developed acute GVHD. The incidence of acute GVHD was associated only with the type of post-transplantation GVHD prophylaxis; none of the other variables included (stem cell source, donor type, age at alloHCT, conditioning regimen and prior history of GVHD) were associated with the frequency of acute GVHD. Twelve patients received post-transplantation cyclophosphamide (PTCy) for GVHD prophylaxis. Patients who received PTCy had a significantly shorter median time to initiation of ICI therapy after alloHCT compared with patients who did not receive PTCy (median 5.1 months compared with 26.6 months). Despite early ICI therapy initiation, patients who received PTCy had a lower observed cumulative incidence of grades 2–4 acute GVHD compared with patients who did not receive PTCy (16% compared with 22%; p=0.7). After controlling for comorbidities and time from alloHCT to ICI therapy initiation, the analysis showed that PTCy was associated with a 90% reduced risk of acute GVHD (HR 0.1, 95% CI 0.02 to 0.6, p=0.01).

Conclusions

ICI therapy for relapsed acute myeloid leukemia/myelodysplastic syndromes after alloHCT may be a safe and feasible option. PTCy appears to decrease the incidence of acute GVHD in this cohort of patients.

PD-1 antibody and ruxolitinib enhances graft-versus-lymphoma effect without increasing acute graft-versus-host disease in mice

Boosting T cell immune response posttransplant with checkpoint inhibitors increases graft-versus-lymphoma (GVL) effects at the cost of increasing acute graft-versus-host disease (aGVHD). A combined targeted therapy is needed to decrease checkpoint inhibitors-induced aGVHD without impairing GVL. We studied whether this competition could be avoided by giving concurrent anti-PD-1 antibody and ruxolitinib in allotransplant mouse models in which recipients were challenged with A20 or EL4 lymphoma cells. Given alone the PD-1 antibody increased GVL but did not improve survival of recipients challenged with A20 cells because of increased deaths from aGVHD. Adding ruxolitinib decreased levels of effector T cells and related cytokines. Tbx21^- T cells had higher PD-1 levels compared with Tbx21⁺ T cells. Ruxolitinib increased PD-1 levels on donor T cells by suppressing Tbx21 expression. Ruxolitinib increased apoptosis of T cells which was reversed by the PD-1 antibody. PD-1 antibody preserved expression of granzyme B and cytotoxicity of T cells which were decreased by ruxolitinib. The net result of combined therapy was increased GVL, no increase in aGVHD and increased survival. The combined therapy improved survival of recipients challenged by A20 cells which expressed high level of PD-L1, but not EL4 cells which do not express PD-L1.

Human amnion-derived mesenchymal stem cells attenuate xenogeneic graft-versus-host disease by preventing T cell activation and proliferation

Acute graft-versus-host disease (GVHD) is characterized by severe tissue damage that is a life-threatening complication of allogeneic hematopoietic stem cell transplantation. Due to their immunosuppressive properties, mesenchymal stem cells (MSC) have been increasingly examined for the treatment of immune-related diseases. We aimed to assess the immunosuppressive effects of human amnion-derived MSC (AMSC) in a xenogeneic GVHD NOD/Shi-scid IL2rγnull mouse model using human peripheral blood mononuclear cells (PBMC). Additionally, we used human bone marrow-derived MSC (BMSC) as comparative controls to determine differences in immunomodulatory functions depending on the MSC origin. Administration of AMSC significantly prolonged survival, and reduced human tumor necrosis factor-α (TNF-α) concentration and percentage of programmed cell death protein-1 receptor (PD-1)⁺CD8⁺ T cell populations compared with in GVHD control mice. Furthermore, colonic inflammation score and percentage of human CD8⁺ T cell populations in AMSC-treated mice were significantly lower than in GVHD control and BMSC-treated mice. Interestingly, gene expression and protein secretion of the PD-1 ligands were higher in AMSC than in BMSC. These findings are the first to demonstrate that AMSC exhibit marked immunosuppression and delay acute GVHD progression by preventing T cell activation and proliferation via the PD-1 pathway.

Novel agents targeting leukemia cells and immune microenvironment for prevention and treatment of relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation

Relapse remains the worst life-threatening complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with acute myeloid leukemia (AML), whose prognosis has been historically dismal. Given the rapid development of genomics and immunotherapies, the interference strategies for AML recurrence have been changing these years. More and more novel targeting agents that have received the U.S. Food and Drug Administration (FDA) approval for de novo AML treatment have been administrated in the salvage or maintenance therapy of post-HSCT relapse. Targeted strategies that regulate the immune microenvironment of and optimize the graft versus leukemia (GVL) effect of immune cells are gradually improved. Such agents not only have been proven to achieve clinical benefits from a single drug, but if combined with classic therapies, can significantly improve the poor prognosis of AML patients who relapse after allo-HSCT. This review will focus on currently available and promising upcoming agents and also discuss the challenges and limitations of targeted therapies in the allogeneic hematopoietic stem cell transplantation community.

Human placenta derived mesenchymal stromal cells alleviate GVHD by promoting the generation of GSH and GST in PD-1+T cells

AIMS

To investigate whether placenta-derived mesenchymal stromal cells (hPMSCs) have immunoregulatory effects on PD-1⁺ T cell generation by controlling ROS production and thus alleviating GVHD.

MAIN METHODS

Flow cytometry was used to analyze the percentage of PD-1⁺ T cells, as well as the generation of ROS, GSH and GST in PD-1⁺ T cells. The expression of GST in the spleen and liver was analyzed by western blotting.

KEY FINDINGS

The percentage of PD-1⁺ T cells was increased, but the ratio of GSH/GSSG was decreased in GVHD patients and the GVHD^high mouse model compared with that in the normal control group. hPMSCs downregulated the level of malondialdehyde (MDA) and upregulated the ratio of GSH/GSSG and the expression of glutathione S transferase (GST) in the plasma, spleen and liver of GVHD mice compared with those of PBS-treated GVHD mice. Further studies showed that the ROS level, as well as the expression of PD-1, in both CD3⁺ and CD4⁺ T cells from the spleen and liver of hPMSC-treated GVHD mice were decreased compared with those observed in PBS-treated mice.

SIGNIFICANCE

hPMSCs downregulated ROS generation by increasing GSH and GST levels and further reduced the expression of PD-1 on T cells, thereby alleviating inflammation in GVHD mice.

Age Distribution of Multiple Functionally Relevant Subsets of CD4+ T Cells in Human Blood Using a Standardized and Validated 14-Color EuroFlow Immune Monitoring Tube

CD4+ T cells comprise multiple functionally distinct cell populations that play a key role in immunity. Despite blood monitoring of CD4+ T-cell subsets is of potential clinical utility, no standardized and validated approaches have been proposed so far. The aim of this study was to design and validate a single 14-color antibody combination for sensitive and reproducible flow cytometry monitoring of CD4+ T-cell populations in human blood to establish normal age-related reference values and evaluate the presence of potentially altered profiles in three distinct disease models—monoclonal B-cell lymphocytosis (MBL), systemic mastocytosis (SM), and common variable immunodeficiency (CVID). Overall, 145 blood samples from healthy donors were used to design and validate a 14-color antibody combination based on extensive reagent testing in multiple cycles of design–testing–evaluation–redesign, combined with in vitro functional studies, gene expression profiling, and multicentric evaluation of manual vs. automated gating. Fifteen cord blood and 98 blood samples from healthy donors (aged 0–89 years) were used to establish reference values, and another 25 blood samples were evaluated for detecting potentially altered CD4 T-cell subset profiles in MBL (n = 8), SM (n = 7), and CVID (n = 10). The 14-color tube can identify ≥89 different CD4+ T-cell populations in blood, as validated with high multicenter reproducibility, particularly when software-guided automated (vs. manual expert-based) gating was used. Furthermore, age-related reference values were established, which reflect different kinetics for distinct subsets: progressive increase of naïve T cells, T-helper (Th)1, Th17, follicular helper T (TFH) cells, and regulatory T cells (Tregs) from birth until 2 years, followed by a decrease of naïve T cells, Th2, and Tregs in older children and a subsequent increase in multiple Th-cell subsets toward late adulthood. Altered and unique CD4+ T-cell subset profiles were detected in two of the three disease models evaluated (SM and CVID). In summary, the EuroFlow immune monitoring TCD4 tube allows fast, automated, and reproducible identification of ≥89 subsets of CD4+ blood T cells, with different kinetics throughout life. These results set the basis for in-depth T-cell monitoring in different disease and therapeutic conditions.

Mechanisms of Leukemia Immune Evasion and Their Role in Relapse After Haploidentical Hematopoietic Cell Transplantation

Over the last decade, the development of multiple strategies to allow the safe transfer from the donor to the patient of high numbers of partially HLA-incompatible T cells has dramatically reduced the toxicities of haploidentical hematopoietic cell transplantation (haplo-HCT), but this was not accompanied by a similar positive impact on the incidence of post-transplantation relapse. In the present review, we will elaborate on how the unique interplay between HLA-mismatched immune system and malignancy that characterizes haplo-HCT may impact relapse biology, shaping the selection of disease variants that are resistant to the “graft-vs.-leukemia” effect. In particular, we will present current knowledge on genomic loss of HLA, a relapse modality first described in haplo-HCT and accounting for a significant proportion of relapses in this setting, and discuss other more recently identified mechanisms of post-transplantation immune evasion and relapse, including the transcriptional downregulation of HLA class II molecules and the enforcement of inhibitory checkpoints between T cells and leukemia. Ultimately, we will review the available treatment options for patients who relapse after haplo-HCT and discuss on how a deeper insight into relapse immunobiology might inform the rational and personalized selection of therapies to improve the largely unsatisfactory clinical outcome of relapsing patients.