Harlan Robins

PD-1 blockade induces responses by inhibiting adaptive immune resistance

Therapies that target the programmed death-1 (PD-1) receptor have shown unprecedented rates of durable clinical responses in patients with various cancer types. One mechanism by which cancer tissues limit the host immune response is via upregulation of PD-1 ligand (PD-L1) and its ligation to PD-1 on antigen-specific CD8+ T cells (termed adaptive immune resistance). Here we show that pre-existing CD8+ T cells distinctly located at the invasive tumour margin are associated with expression of the PD-1/PD-L1 immune inhibitory axis and may predict response to therapy. We analysed samples from 46 patients with metastatic melanoma obtained before and during anti-PD-1 therapy (pembrolizumab) using quantitative immunohistochemistry, quantitative multiplex immunofluorescence, and next-generation sequencing for T-cell antigen receptors (TCRs). In serially sampled tumours, patients responding to treatment showed proliferation of intratumoral CD8+ T cells that directly correlated with radiographic reduction in tumour size. Pre-treatment samples obtained from responding patients showed higher numbers of CD8-, PD-1- and PD-L1-expressing cells at the invasive tumour margin and inside tumours, with close proximity between PD-1 and PD-L1, and a more clonal TCR repertoire. Using multivariate analysis, we established a predictive model based on CD8 expression at the invasive margin and validated the model in an independent cohort of 15 patients. Our findings indicate that tumour regression after therapeutic PD-1 blockade requires pre-existing CD8+ T cells that are negatively regulated by PD-1/PD-L1-mediated adaptive immune resistance.

A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans

The tumor suppressor p53 gene is mutated in minimally half of all cancers. It is therefore reasonable to assume that naturally occurring polymorphic genetic variants in the p53 stress response pathway might determine an individuals susceptibility to cancer. A central node in the p53 pathway is the MDM2 protein, a direct negative regulator of p53. In this report, a single nucleotide polymorphism (SNP309) is found in the MDM2 promoter and is shown to increase the affinity of the transcriptional activator Sp1, resulting in higher levels of MDM2 RNA and protein and the subsequent attenuation of the p53 pathway. In humans, SNP309 is shown to associate with accelerated tumor formation in both hereditary and sporadic cancers. A model is proposed whereby SNP309 serves as a rate-limiting event in carcinogenesis.

Comprehensive assessment of T-cell receptor β-chain diversity in αβ T cells

The adaptive immune system uses several strategies to generate a repertoire of T- and B-cell antigen receptors with sufficient diversity to recognize the universe of potential pathogens. In alphabeta T cells, which primarily recognize peptide antigens presented by major histocompatibility complex molecules, most of this receptor diversity is contained within the third complementarity-determining region (CDR3) of the T-cell receptor (TCR) alpha and beta chains. Although it has been estimated that the adaptive immune system can generate up to 10(16) distinct alphabeta pairs, direct assessment of TCR CDR3 diversity has not proved amenable to standard capillary electrophoresis-based DNA sequencing. We developed a novel experimental and computational approach to measure TCR CDR3 diversity based on single-molecule DNA sequencing, and used this approach to determine the CDR3 sequence in millions of rearranged TCRbeta genes from T cells of 2 adults. We find that total TCRbeta receptor diversity is at least 4-fold higher than previous estimates, and the diversity in the subset of CD45RO(+) antigen-experienced alphabeta T cells is at least 10-fold higher than previous estimates. These methods should prove valuable for assessment of alphabeta T-cell repertoire diversity after hematopoietic cell transplantation, in states of congenital or acquired immunodeficiency, and during normal aging.

MDM2 SNP309 Accelerates Tumor Formation in a Gender-Specific and Hormone-Dependent Manner

The importance of the p53 stress response pathway in the suppression of tumor formation is well documented. In a previous report, a single nucleotide polymorphism (SNP309 T/G) was found in the promoter of the MDM2 gene resulting in higher levels of MDM2 RNA and protein and, consequently, in the attenuation of the p53 pathway both in vitro and in vivo. As the SNP309 locus is found in a region of the MDM2 promoter, which is regulated by hormonal signaling pathways, and the G-allele of SNP309 increases the affinity of a well-described cotranscriptional activator of nuclear hormone receptors (i.e., Sp1), the hypothesis that the SNP309 locus could alter the effects of hormones on tumorigenesis was tested in vivo in humans. Data obtained from patients with three different sporadic cancers, from four independent case studies, support this hypothesis, providing an example for the genetic basis of gender differences in cancer and showing that the genotype at a specific locus can affect how hormones, like estrogen, affect tumorigenesis in humans.

Overlap and Effective Size of the Human CD8+ T Cell Receptor Repertoire

Deep sequencing of the T cell receptor repertoires of seven healthy adults reveals that the adaptive immune system is far less diverse than expected and the person-to-person overlap is thousands of times larger. Not So Diverse After All You never know what nasty microbe lurks around the corner. To guard against these potential foes, our immune cells produce a vast variety of antibody and T cell receptor (TCR) shapes ready to recognize these pathogens. This diversity is manufactured by gene rearrangement, with fragments from the so-called V, D, and J gene groups joined together to form an array of sequences, much as colored beads can be arranged on a string to make many combinations. With several choices for each of the V, D, and J fragments, supplemented with a few random nucleotides inserted at the junctions, an astronomical number of different arrangements can theoretically be created. Originally, this was thought to be a random process, but Robins et al., by high-throughput genome sequencing of seven people, show that the generation of immune diversity is actually selective, creating an unexpectedly small assortment of TCRs that is similar in different people. By analyzing blood samples containing millions of T cells from healthy donors and sequencing the TCRs from each donor’s set of naïve and memory T cells, the authors revealed that the sequences of the TCRβ subunits in each subject are not randomly distributed. Instead, certain D and J segments preferentially associated with each other. The number of nucleotides inserted at junction sites between the segments was also smaller than expected. As a result, the actual repertoire of each person’s T cells is a fraction of that predicted by a computer model assuming random rearrangement, and the overlap between donors’ T cells is several orders of magnitude greater. If the rearrangements were truly random, two unrelated adults would only be expected to share on average five TCRβ sequences, of a total 3 million, but the overlap turned out to be more than 10,000 sequences. The authors also overturn another assumption in the field. It had been thought that a random set of V-D-J combinations was generated and then, by deletion and selection in the thymus of cells carrying less useful combinations, only a subset matured, forming the final immune repertoire. Instead, the authors show that the T cell repertoire is limited and biased from the time of the original V-D-J rearrangement during cell development. Now that deep sequencing of these key immune regions in individual genomes is achievable, we will be able to compare TCR sequences and antibodies in healthy individuals with those of patients with autoimmune disorders, or of transplant recipients suffering from graft-versus-host disease. The results may help to understand these illnesses and to look for ways to modify patients’ T cell repertoires for treatment or prevention of autoimmunity or to enhance compatibility between transplant donors and recipients. Diversity in T lymphocyte antigen receptors is generated by somatic rearrangement of T cell receptor (TCR) genes and is concentrated within the third complementarity-determining region 3 (CDR3) of each chain of the TCR heterodimer. We sequenced the CDR3 regions from millions of rearranged TCR β chain genes in naïve and memory CD8+ T cells of seven adults. The CDR3 sequence repertoire realized in each individual is strongly biased toward specific Vβ-Jβ pair utilization, dominated by sequences containing few inserted nucleotides, and drawn from a defined subset comprising less than 0.1% of the estimated 5 × 1011 possible sequences. Surprisingly, the overlap in the naïve CD8+ CDR3 sequence repertoires of any two of the individuals is ~7000-fold larger than predicted and appears to be independent of the degree of human leukocyte antigen matching.

Suppression of immediate-early viral gene expression by herpesvirus-coded microRNAs: Implications for latency

A quantitative algorithm was developed and applied to predict target genes of microRNAs encoded by herpesviruses. Although there is almost no conservation among microRNAs of different herpesvirus subfamilies, a common pattern of regulation emerged. The algorithm predicts that herpes simplex virus 1, human cytomegalovirus, Epstein–Barr virus, and Kaposis sarcoma-associated herpesvirus all employ microRNAs to suppress expression of their own genes, including their immediate-early genes. In the case of human cytomegalovirus, a virus-coded microRNA, miR-112-1, was predicted to target the viral immediate-early protein 1 mRNA. To test this prediction, mutant viruses were generated that were unable to express the microRNA, or encoded an immediate-early 1 mRNA lacking its target site. Analysis of RNA and protein within infected cells demonstrated that miR-UL112-1 inhibits expression of the major immediate-early protein. We propose that herpesviruses use microRNA-mediated suppression of immediate-early genes as part of their strategy to enter and maintain latency.

Using synthetic templates to design an unbiased multiplex PCR assay

T and B cell receptor loci undergo combinatorial rearrangement, generating a diverse immune receptor repertoire, which is vital for recognition of potential antigens. Here we use a multiplex PCR with a mixture of primers targeting the rearranged variable and joining segments to capture receptor diversity. Differential hybridization kinetics can introduce significant amplification biases that alter the composition of sequence libraries prepared by multiplex PCR. Using a synthetic immune receptor repertoire, we identify and minimize such biases and computationally remove residual bias after sequencing. We apply this method to a multiplex T cell receptor gamma sequencing assay. To demonstrate accuracy in a biological setting, we apply the method to monitor minimal residual disease in acute lymphoblastic leukaemia patients. A similar methodology can be extended to any adaptive immune locus.

High-Throughput Sequencing Detects Minimal Residual Disease in Acute T Lymphoblastic Leukemia

High-throughput sequencing can detect minimal residual disease comparable to multiparametric flow cytometry in T-ALL patients. Finding a Needle in a Haystack Even in seemingly successful cancer therapy, a small number of cells can survive treatment and persist in patients in remission. This minimal residual disease (MRD) is a major cause of cancer relapse, and until recently was undetectable. New ways to track MRD can determine whether cancer has been eradicated, compare the efficacy of different treatments, monitor patient remission status, and aid in treatment selection. Wu et al. use high-throughput sequencing (HTS) of lymphoid receptor genes to track MRD in T-lineage acute lymphoblastic leukemia/lymphoma (T-ALL). The authors sequence the variable regions of two T cell antigen receptor genes (TCRB and TCRG) using multiplexed polymerase chain reaction. First, they identified clonal T cell receptor (TCR) sequences in individual T-ALL patients and then looked in the same patients after treatment. Their strategy identified clonality at diagnosis in most cases and also detected subsequent MRD. In a subset of cases, HTS detected MRD in patients where it was not detected by flow cytometry, which is currently used in the clinic. Thus, HTS may lower the threshold of detection for MRD and affect treatment decisions. High-throughput sequencing (HTS) of lymphoid receptor genes is an emerging technology that can comprehensively assess the diversity of the immune system. Here, we applied HTS to the diagnosis of T-lineage acute lymphoblastic leukemia/lymphoma. Using 43 paired patient samples, we then assessed minimal residual disease (MRD) at day 29 after treatment. The variable regions of TCRB and TCRG were sequenced using an Illumina HiSeq platform after performance of multiplexed polymerase chain reaction, which targeted all potential V-J rearrangement combinations. Pretreatment samples were used to define clonal T cell receptor (TCR) complementarity-determining region 3 (CDR3) sequences, and paired posttreatment samples were evaluated for MRD. Abnormal T lymphoblast identification by multiparametric flow cytometry was concurrently performed for comparison. We found that TCRB and TCRG HTS not only identified clonality at diagnosis in most cases (31 of 43 for TCRB and 27 of 43 for TCRG) but also detected subsequent MRD. As expected, HTS of TCRB and TCRG identified MRD that was not detected by flow cytometry in a subset of cases (25 of 35 HTS compared with 13 of 35, respectively), which highlights the potential of this technology to define lower detection thresholds for MRD that could affect clinical treatment decisions. Thus, next-generation sequencing of lymphoid receptor gene repertoire may improve clinical diagnosis and subsequent MRD monitoring of lymphoproliferative disorders.

Immune surveillance by CD8αα + skin-resident T cells in human herpes virus infection

Most herpes simplex virus 2 (HSV-2) reactivations in humans are subclinical and associated with rapid expansion and containment of virus. Previous studies have shown that CD8+ T cells persist in genital skin and mucosa at the dermal–epidermal junction (DEJ)—the portal of neuronal release of reactivating virus—for prolonged time periods after herpes lesions are cleared. The phenotype and function of this persistent CD8+ T-cell population remain unknown. Here, using cell-type-specific laser capture microdissection, transcriptional profiling and T-cell antigen receptor β-chain (TCRβ) genotyping on sequential genital skin biopsies, we show that CD8αα+ T cells are the dominant resident population of DEJ CD8+ T cells that persist at the site of previous HSV-2 reactivation. CD8αα+ T cells located at the DEJ lack chemokine-receptor expression required for lymphocyte egress and recirculation, express gene signatures of T-cell activation and antiviral activity, and produce cytolytic granules during clinical and virological quiescent time periods. Sequencing of the TCR β-chain repertoire reveals that the DEJ CD8αα+ T cells are oligoclonal with diverse usage of TCR variable-β genes, which differ from those commonly described for mucosa-associated invariant T cells and natural killer T cells. Dominant clonotypes are shown to overlap among multiple recurrences over a period of two-and-a-half years. Episodes of rapid asymptomatic HSV-2 containment were also associated with a high CD8 effector-to-target ratio and focal enrichment of CD8αα+ T cells. These studies indicate that DEJ CD8αα+ T cells are tissue-resident cells that seem to have a fundamental role in immune surveillance and in initial containment of HSV-2 reactivation in human peripheral tissue. Elicitation of CD8αα+ T cells may be a critical component for developing effective vaccines against skin and mucosal infections.

CTLA4 Blockade Broadens the Peripheral T-Cell Receptor Repertoire

Purpose: To evaluate the immunomodulatory effects of cytotoxic T–lymphocyte-associated protein 4 (CTLA4) blockade with tremelimumab in peripheral blood mononuclear cells (PBMC). Experimental Design: We used next-generation sequencing to study the complementarity-determining region 3 (CDR3) from the rearranged T-cell receptor (TCR) variable beta (V-beta) in PBMCs of 21 patients, at baseline and 30 to 60 days after receiving tremelimumab. Results: After receiving tremelimumab, there was a median of 30% increase in unique productive sequences of TCR V-beta CDR3 in 19 out of 21 patients, and a median decrease of 30% in only 2 out of 21 patients. These changes were significant for richness (P = 0.01) and for Shannon index diversity (P = 0.04). In comparison, serially collected PBMCs from four healthy donors did not show a significant change in TCR V-beta CDR3 diversity over 1 year. There was a significant difference in the total unique productive TCR V-beta CDR3 sequences between patients experiencing toxicity with tremelimumab compared with patients without toxicity (P = 0.05). No relevant differences were noted between clinical responders and nonresponders. Conclusions: CTLA4 blockade with tremelimumab diversifies the peripheral T-cell pool, representing a pharmacodynamic effect of how this class of antibodies modulates the human immune system. Clin Cancer Res; 20(9); 2424–32. ©2014 AACR.