PD-1 Expression on Intratumoral Regulatory T Cells Is Associated with Lack of Benefit from Anti-PD-1 Therapy in Metastatic Clear-Cell Renal Cell Carcinoma Patients

PURPOSE

Programmed cell death protein 1 (PD-1) expression on CD8+TIM-3-LAG-3- tumor-infiltrating cells predicts positive response to PD-1 blockade in metastatic clear-cell renal cell carcinoma (mccRCC). Because inhibition of PD-1 signaling in regulatory T cells (Treg) augments their immunosuppressive function, we hypothesized that PD-1 expression on tumor-infiltrating Tregs would predict resistance to PD-1 inhibitors.

EXPERIMENTAL DESIGN

PD-1+ Tregs were phenotyped using multiparametric immunofluorescence in ccRCC tissues from the CheckMate-025 trial (nivolumab: n = 91; everolimus: n = 90). Expression of CD8, PD-1, TIM-3, and LAG-3 was previously determined (Ficial and colleagues, 2021). Clinical endpoints included progression-free survival (PFS), overall survival (OS), and objective response rate (ORR).

RESULTS

In the nivolumab (but not everolimus) arm, high percentage of PD-1+ Tregs was associated with shorter PFS (3.19 vs. 5.78 months; P = 0.021), shorter OS (18.1 vs. 27.7 months; P = 0.013) and marginally lower ORR (12.5% vs. 31.3%; P = 0.059). An integrated biomarker (PD-1 Treg/CD8 ratio) was developed by calculating the ratio between percentage of PD-1+Tregs (marker of resistance) and percentage of CD8+PD-1+TIM-3-LAG-3- cells (marker of response). In the nivolumab (but not everolimus) arm, patients with high PD-1 Treg/CD8 ratio experienced shorter PFS (3.48 vs. 9.23 months; P < 0.001), shorter OS (18.14 vs. 38.21 months; P < 0.001), and lower ORR (15.69% vs. 40.00%; P = 0.009). Compared with the individual biomarkers, the PD-1 Treg/CD8 ratio showed improved ability to predict outcomes to nivolumab versus everolimus.

CONCLUSIONS

PD-1 expression on Tregs is associated with resistance to PD-1 blockade in mccRCC, suggesting that targeting Tregs may synergize with PD-1 inhibition. A model that integrates PD-1 expression on Tregs and CD8+TIM-3-LAG-3- cells has higher predictive value.

The B7:CD28 family and friends: Unraveling coinhibitory interactions

Immune responses must be tightly regulated to ensure both optimal protective immunity and tolerance. Costimulatory pathways within the B7:CD28 family provide essential signals for optimal T cell activation and clonal expansion. They provide crucial inhibitory signals that maintain immune homeostasis, control resolution of inflammation, regulate host defense, and promote tolerance to prevent autoimmunity. Tumors and chronic pathogens can exploit these pathways to evade eradication by the immune system. Advances in understanding B7:CD28 pathways have ushered in a new era of immunotherapy with effective drugs to treat cancer, autoimmune diseases, infectious diseases, and transplant rejection. Here, we discuss current understanding of the mechanisms underlying the coinhibitory functions of CTLA-4, PD-1, PD-L1:B7-1 and PD-L2:RGMb interactions and less studied B7 family members, including HHLA2, VISTA, BTNL2, and BTN3A1, as well as their overlapping and unique roles in regulating immune responses, and the therapeutic potential of these insights.

Tracking tumor-specific CD8+ T cell responses

In a recent article, Puig-Saus et al. computationally predict and experimentally validate neoantigen-specific T cell responses in patients with melanoma. They identify a restricted set of neoantigens recognized by polyclonal CD8⁺ T cells as a unique feature of anti-PD-1 responders and engineer autologous tumor-responsive T cells expressing neoantigen-specific TCRs, providing proof-of-concept for future cellular therapies.

Abstract 3271: Multiomic meta-analysis of differential response to PD-1 and CTLA-4 blockade in metastatic melanoma

Background: While CTLA-4 and PD-1 immune-checkpoint blockade (ICB) have revolutionized melanoma treatment, these treatments have different mechanisms, response rates, and toxicities. Differential predictors of response are poorly characterized. Combination ICB has the highest response rates but also much higher toxicity, and which patients to treat with single agent vs. combination ICB is controversial. In this study, we set out to understand the differential biology of anti-CTLA-4 and anti-PD-1 by integrating transcriptomic and clinical characterization from large cohorts of patients with metastatic melanoma treated with anti-CTLA-4, anti-PD-1, or combination blockade.

Methods: We performed a standardized meta-analysis of all available cohorts of ICB-treated (anti-PD-1 alone, anti-CTLA-4 alone, and combination) melanoma patients with sequencing of pretreatment tumor and clinical annotations (n=572; 268 evaluated post quality-control filtering, cutaneous). Raw data in the form of FASTQs were obtained for all cohorts, and data were reprocessed using standardized pipelines. Immune infiltrate was characterized using single-sample gene set enrichment analysis (ssGSEA) scores from 18 immune cell type signatures, and GSEA was performed on differentially expressed genes between responders and non-responders for each treatment cohort accounting for differences in immune infiltrate. To dissect the cell types and drivers of nominated signatures, we analyzed scRNAseq from a separate cohort of pretreatment metastatic melanoma.

Results: We found that immune infiltrate was strongly predictive of response to combination blockade (OR=6.16, p&lt;0.05) but had a weaker signal in the monotherapy context (anti-PD-1 OR=1.42, n.s.; anti-CTLA-4 OR=1.10, n.s.). Among samples with a high degree of immune-infiltrate treated with either anti-CTLA-4 and anti-PD-1, non-responders were enriched in hypoxia (avg. NES=-1.38, FDR&lt;0.05) and epithelial-mesenchymal transition (avg. NES=-2.32, FDR&lt;0.05) gene signatures. Preliminary analysis of the single cell cohort shows a specific population of myeloid cells (MW p&lt;0.05) and exhausted CD8+ T cells (MW p&lt;0.05) increased in pretreatment hypoxic tumors.

Conclusion: High rates of response to combination in patients with high levels of immune infiltrate suggests that immune high patients may differentially benefit from combination blockade. Identifying features of non-responding patients stratified by immune infiltrate can lead to new biological insights into ICB.

Citation Format: Amy Y. Huang, Natalie Vokes, Cora Ricker, Tyler Aprati, Emily Robitschek, Jiekun Yang, Li-Lun Ho, Kyriakitsa Galani, Kelly P. Burke, Giuseppe Tarantino, Jiajia Chen, Arlene H. Sharpe, Eliezer M. Van Allen, Manolis Kellis, Genevieve M. Boland, David Liu. Multiomic meta-analysis of differential response to PD-1 and CTLA-4 blockade in metastatic melanoma [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 3271.

Immune checkpoint receptors in autoimmunity

Immune checkpoint receptors such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), and T cell immunoglobulin and ITIM domain (TIGIT) have distinct and overlapping inhibitory functions that regulate Tcell activation, differentiation, and function. These inhibitory receptors also mediate tolerance, and dysregulation of these receptors can result in a breach of tolerance and the development of autoimmune syndromes. Similarly, antibody blockade of immune checkpoint receptors or their ligands for cancer immunotherapy may trigger a spectrum of organ inflammation that resembles autoimmunity, termed immune-related adverse events (irAE). In this review, we discuss recent advances in the regulation of autoimmunity by immune checkpoint receptors. We highlight coordinated gene expression programs linking checkpoint receptors, heterogeneity within autoreactive T-cell populations, parallels between irAE and autoimmunity, and bidirectional functional interactions between immune checkpoint receptors and their ligands.

When killers become thieves: Trogocytosed PD-1 inhibits NK cells in cancer

Trogocytosis modulates immune responses, with still unclear underlying molecular mechanisms. Using leukemia mouse models, we found that lymphocytes perform trogocytosis at high rates with tumor cells. While performing trogocytosis, both Natural Killer (NK) and CD8+ T cells acquire the checkpoint receptor PD-1 from leukemia cells. In vitro and in vivo investigation revealed that PD-1 on the surface of NK cells, rather than being endogenously expressed, was derived entirely from leukemia cells in a SLAM receptor-dependent fashion. PD-1 acquired via trogocytosis actively suppressed NK cell antitumor immunity. PD-1 trogocytosis was corroborated in patients with clonal plasma cell disorders, where NK cells that stained for PD-1 also stained for tumor cell markers. Our results, in addition to shedding light on a previously unappreciated mechanism underlying the presence of PD-1 on NK and cytotoxic T cells, reveal the immunoregulatory effect of membrane transfer occurring when immune cells contact tumor cells.

Understanding adverse events of immunotherapy: A mechanistic perspective

The treatment of many cancers has been revolutionized by immune checkpoint blockade (ICB) as a standard-of-care therapeutic. Despite many successes, a large proportion of patients treated with ICB agents experience immune-related adverse events (irAEs) in the form of clinical autoimmunity, ranging from mild to life threatening, that can limit cancer treatment. A mechanistic understanding of these irAEs is required to better treat or prevent irAEs and to predict those patients who are susceptible to irAEs. We propose several mechanisms that may contribute to the generation of irAEs: (1) preexisting susceptibility to autoimmunity, (2) aberrant presentation of “self” by the tumor, and (3) loss of tolerance driven by the tumor or tissue microenvironment.

Progressive immune dysfunction with advancing disease stage in renal cell carcinoma

The tumor immune microenvironment plays a critical role in cancer progression and response to immunotherapy in clear cell renal cell carcinoma (ccRCC), yet the composition and phenotypic states of immune cells in this tumor are incompletely characterized. We performed single-cell RNA and T cell receptor sequencing on 164,722 individual cells from tumor and adjacent non-tumor tissue in patients with ccRCC across disease stages: early, locally advanced, and advanced/metastatic. Terminally exhausted CD8⁺ T cells were enriched in metastatic disease and were restricted in T cell receptor diversity. Within the myeloid compartment, pro-inflammatory macrophages were decreased, and suppressive M2-like macrophages were increased in advanced disease. Terminally exhausted CD8⁺ T cells and M2-like macrophages co-occurred in advanced disease and expressed ligands and receptors that support T cell dysfunction and M2-like polarization. This immune dysfunction circuit is associated with a worse prognosis in external cohorts and identifies potentially targetable immune inhibitory pathways in ccRCC.

Single-cell analyses characterize circulating anti-tumor CD8+ T cells in mice and humans and identify markers for their enrichment

The ability to monitor anti-tumor CD8+ T cell responses in the blood has tremendous therapeutic potential, but is currently challenging due to the limited number of reagents to track antigen-specific T cells. Here, we used paired single-cell RNA sequencing and T cell receptor (TCR) sequencing to detect and characterize “tumor matching” (TM) CD8+ T cells in the blood of mice with MC38 tumors or melanoma patients using the TCR as a molecular barcode. TM cells showed increased activation compared to non-matching T cells in blood, and appeared less exhausted than matching counterparts in tumor. Importantly, PD-1, which has been used to identify putative circulating anti-tumor CD8+ T cells, showed poor sensitivity for identifying TM cells in both mice and humans. By leveraging the transcriptome, we identified candidate cell surface marker panels for TM cells in mice and melanoma patients, and validated CX3CR1, NKG2D, and CD39 proteins in mice. Combinations of markers performed better than single markers in identifying TM cells from non-TM cells in the blood, providing a platform to potentially track TM cells based on surface markers instead of the TCR. These data demonstrate that the TCR can be used to identify tumor-relevant populations for comprehensive characterization, reveal unique transcriptional properties of TM cells, and develop marker panels for tracking and analysis of these cells.

The PD-1 Pathway Regulates Development and Function of Memory CD8+ T Cells following Respiratory Viral Infection

The PD-1 pathway regulates dysfunctional T cells in chronic infection and cancer, but the role of this pathway during acute infection remains less clear. Here, we demonstrate that PD-1 signals are needed for optimal memory. Mice deficient in the PD-1 pathway exhibit impaired CD8⁺ T cell memory following acute influenza infection, including reduced virus-specific CD8⁺ T cell numbers and compromised recall responses. PD-1 blockade during priming leads to similar differences early post-infection but without the defect in memory formation, suggesting that timing and/or duration of PD-1 blockade could be tailored to modulate host responses. Our studies reveal a role for PD-1 as an integrator of CD8⁺ T cell signals that promotes CD8⁺ T cell memory formation and suggest PD-1 continues to fine-tune CD8⁺ T cells after they migrate into non-lymphoid tissues. These findings have important implications for PD-1-based immunotherapy, in which PD-1 inhibition may influence memory responses in patients.

Single-cell analyses identify circulating anti-tumor CD8 T cells and markers for their enrichment

The ability to monitor anti-tumor CD8⁺ T cell responses in the blood has tremendous therapeutic potential. Here, we used paired single-cell RNA and TCR sequencing to detect and characterize “tumor-matching” (TM) CD8⁺ T cells in the blood of mice with MC38 tumors or melanoma patients using the TCR as a molecular barcode. TM cells showed increased activation compared with nonmatching T cells in blood and were less exhausted than matching cells in tumors. Importantly, PD-1, which has been used to identify putative circulating anti-tumor CD8⁺ T cells, showed poor sensitivity for identifying TM cells. By leveraging the transcriptome, we identified candidate cell surface markers for TM cells in mice and patients and validated NKG2D, CD39, and CX3CR1 in mice. These data show that the TCR can be used to identify tumor-relevant cells for characterization, reveal unique transcriptional properties of TM cells, and develop marker panels for tracking and analysis of these cells.

Abstract PO016: Single-cell analyses characterize circulating anti-tumor CD8 T cells and identify markers for their isolation

The ability to monitor anti-tumor CD8+ T cell responses in the blood has tremendous therapeutic potential. Here, we used paired single-cell RNA sequencing and T cell receptor (TCR) sequencing to detect and characterize “tumor matching” (TM) CD8+ T cells in the blood of mice with MC38 tumors and melanoma patients using the TCR as a molecular barcode. TM cells showed increased activation compared to non-matching T cells in blood, and appeared less exhausted than matching counterparts in tumor. Importantly, PD-1, which has been used to identify putative circulating anti-tumor CD8+ T cells, showed poor sensitivity for identifying TM cells. By leveraging the transcriptome we identified candidate cell surface marker panels for TM cells in mice and melanoma patients, and validated markers in mice. Here, using combinations of markers provided better performance than single markers in identifying TM cells from non-TM cells in the blood. These data demonstrate that the TCR can be used to identify tumor-relevant populations for comprehensive characterization, reveal unique transcriptional properties of TM cells, and develop marker panels for tracking and analysis of these cells.

Citation Format: Kristen E. Pauken, Osmaan Shahid, Kaitlyn A. Lagattuta, Kelly M. Mahuron, Jacob M. Luber, Margaret M. Lowe, Linglin Huang, Conor Delaney, Jaclyn M. Long, Megan E. Fung, Kathleen Newcomer, Katy K. Tsai, Melissa Chow, Samantha Guinn, Juhi R. Kuchroo, Kelly P. Burke, Jason M. Schenkel, Michael D. Rosenblum, Adil I. Daud, Arlene H. Sharpe, Meromit Singer. Single-cell analyses characterize circulating anti-tumor CD8 T cells and identify markers for their isolation [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO016.

Transcriptional mediators of treatment resistance in lethal prostate cancer

Metastatic castration-resistant prostate cancer is typically lethal, exhibiting intrinsic or acquired resistance to second-generation androgen-targeting therapies and minimal response to immune checkpoint inhibitors¹. Cellular programs driving resistance in both cancer and immune cells remain poorly understood. We present single-cell transcriptomes from 14 patients with advanced prostate cancer, spanning all common metastatic sites. Irrespective of treatment exposure, adenocarcinoma cells pervasively coexpressed multiple androgen receptor isoforms, including truncated isoforms hypothesized to mediate resistance to androgen-targeting therapies^2,3. Resistance to enzalutamide was associated with cancer cell-intrinsic epithelial-mesenchymal transition and transforming growth factor-β signaling. Small cell carcinoma cells exhibited divergent expression programs driven by transcriptional regulators promoting lineage plasticity and HOXB5, HOXB6 and NR1D2 (refs. ^4-6). Additionally, a subset of patients had high expression of dysfunction markers on cytotoxic CD8⁺ T cells undergoing clonal expansion following enzalutamide treatment. Collectively, the transcriptional characterization of cancer and immune cells from human metastatic castration-resistant prostate cancer provides a basis for the development of therapeutic approaches complementing androgen signaling inhibition.

Genomic correlates of response to immune checkpoint blockade

Despite impressive durable responses, immune checkpoint inhibitors do not provide a long-term benefit to the majority of patients with cancer. Understanding genomic correlates of response and resistance to checkpoint blockade may enhance benefits for patients with cancer by elucidating biomarkers for patient stratification and resistance mechanisms for therapeutic targeting. Here we review emerging genomic markers of checkpoint blockade response, including those related to neoantigens, antigen presentation, DNA repair, and oncogenic pathways. Compelling evidence also points to a role for T cell functionality, checkpoint regulators, chromatin modifiers, and copy-number alterations in mediating selective response to immune checkpoint blockade. Ultimately, efforts to contextualize genomic correlates of response into the larger understanding of tumor immune biology will build a foundation for the development of novel biomarkers and therapies to overcome resistance to checkpoint blockade.

Immunogenomic analyses associate immunological alterations with mismatch repair defects in prostate cancer

BACKGROUND. Understanding the integrated immunogenomic landscape of advanced prostate cancer (APC) could impact stratified treatment selection.

METHODS. Defective mismatch repair (dMMR) status was determined by either loss of mismatch repair protein expression on IHC or microsatellite instability (MSI) by PCR in 127 APC biopsies from 124 patients (Royal Marsden [RMH] cohort); MSI by targeted panel next-generation sequencing (MSINGS) was then evaluated in the same cohort and in 254 APC samples from the Stand Up To Cancer/Prostate Cancer Foundation (SU2C/PCF). Whole exome sequencing (WES) data from this latter cohort were analyzed for pathogenic MMR gene variants, mutational load, and mutational signatures. Transcriptomic data, available for 168 samples, was also performed.

RESULTS. Overall, 8.1% of patients in the RMH cohort had some evidence of dMMR, which associated with decreased overall survival. Higher MSINGS scores associated with dMMR, and these APCs were enriched for higher T cell infiltration and PD-L1 protein expression. Exome MSINGS scores strongly correlated with targeted panel MSINGS scores (r = 0.73, P < 0.0001), and higher MSINGS scores associated with dMMR mutational signatures in APC exomes. dMMR mutational signatures also associated with MMR gene mutations and increased immune cell, immune checkpoint, and T cell–associated transcripts. APC with dMMR mutational signatures overexpressed a variety of immune transcripts, including CD200R1, BTLA, PD-L1, PD-L2, ADORA2A, PIK3CG, and TIGIT.

CONCLUSION. These data could impact immune target selection, combination therapeutic strategy selection, and selection of predictive biomarkers for immunotherapy in APC.

FUNDING. We acknowledge funding support from Movember, Prostate Cancer UK, The Prostate Cancer Foundation, SU2C, and Cancer Research UK.

Real-time Genomic Characterization of Advanced Pancreatic Cancer to Enable Precision Medicine

Clinically relevant subtypes exist for pancreatic ductal adenocarcinoma (PDAC), but molecular characterization is not yet standard in clinical care. We implemented a biopsy protocol to perform time-sensitive whole-exome sequencing and RNA sequencing for patients with advanced PDAC. Therapeutically relevant genomic alterations were identified in 48% (34/71) and pathogenic/likely pathogenic germline alterations in 18% (13/71) of patients. Overall, 30% (21/71) of enrolled patients experienced a change in clinical management as a result of genomic data. Twenty-six patients had germline and/or somatic alterations in DNA-damage repair genes, and 5 additional patients had mutational signatures of homologous recombination deficiency but no identified causal genomic alteration. Two patients had oncogenic in-frame BRAF deletions, and we report the first clinical evidence that this alteration confers sensitivity to MAPK pathway inhibition. Moreover, we identified tumor/stroma gene expression signatures with clinical relevance. Collectively, these data demonstrate the feasibility and value of real-time genomic characterization of advanced PDAC.Significance: Molecular analyses of metastatic PDAC tumors are challenging due to the heterogeneous cellular composition of biopsy specimens and rapid progression of the disease. Using an integrated multidisciplinary biopsy program, we demonstrate that real-time genomic characterization of advanced PDAC can identify clinically relevant alterations that inform management of this difficult disease. Cancer Discov; 8(9); 1096-111. ©2018 AACR.See related commentary by Collisson, p. 1062This article is highlighted in the In This Issue feature, p. 1047.

Genomic Approaches to Understanding Response and Resistance to Immunotherapy

Immunotherapy has led to a paradigm shift in the treatment of some malignancies, providing long-term, durable responses for patients with advanced cancers. However, such therapy has benefited only a subset of patients, with some patients failing to respond to treatment at all and others achieving a limited response followed by tumor progression. Understanding factors contributing to an effective response and further elucidating mechanisms of resistance will be crucial as these therapies are applied more broadly. Genomics-based approaches have significantly advanced the study of response and resistance to immunotherapy in general, and to immune checkpoint blockade more specifically. Here, we review how genomic and transcriptomic approaches have identified both somatic and germline positive correlates of response, including high mutational/neoantigen load and low intratumoral heterogeneity, among others. The genomic analysis of resistant tumors has additionally identified crucial factors involved in resistance to immune checkpoint blockade, including loss of PTEN and upregulation of other immune checkpoints. Overall, the continued use of genomic techniques at the point of care, combined with appropriate functional studies, would ideally lead to a better understanding of why certain patients respond to immune-based therapies, allowing clinicians to identify the subset of patients likely to benefit from such therapy, and potentially providing insight into how other therapies may be added in combination to increase the number of patients who may benefit from immunotherapy. Clin Cancer Res; 22(23); 5642-50. ©2016 AACR.

Genomic Approaches to Understanding Response and Resistance to Immunotherapy

Immunotherapy has led to a paradigm shift in the treatment of some malignancies, providing long-term, durable responses for patients with advanced cancers. However, such therapy has benefited only a subset of patients, with some patients failing to respond to treatment at all and others achieving a limited response followed by tumor progression. Understanding factors contributing to an effective response and further elucidating mechanisms of resistance will be crucial as these therapies are applied more broadly. Genomics-based approaches have significantly advanced the study of response and resistance to immunotherapy in general, and to immune checkpoint blockade more specifically. Here, we review how genomic and transcriptomic approaches have identified both somatic and germline positive correlates of response, including high mutational/neoantigen load and low intratumoral heterogeneity, among others. The genomic analysis of resistant tumors has additionally identified crucial factors involved in resistance to immune checkpoint blockade, including loss of PTEN and upregulation of other immune checkpoints. Overall, the continued use of genomic techniques at the point of care, combined with appropriate functional studies, would ideally lead to a better understanding of why certain patients respond to immune-based therapies, allowing clinicians to identify the subset of patients likely to benefit from such therapy, and potentially providing insight into how other therapies may be added in combination to increase the number of patients who may benefit from immunotherapy. Clin Cancer Res; 22(23); 5642-50. ©2016 AACR.

Immunogenicity and cross-reactivity of a representative ancestral sequence in hepatitis C virus infection

Vaccines designed to prevent or to treat hepatitis C viral infection must achieve maximum cross-reactivity against widely divergent circulating strains. Rational approaches for sequence selection to maximize immunogenicity and minimize genetic distance across circulating strains may enhance vaccine induction of optimal cytotoxic T cell responses. We assessed T cell recognition of potential hepatitis C virus (HCV) vaccine sequences generated using three rational approaches: combining epitopes with predicted tight binding to the MHC, consensus sequence (most common amino acid at each position), and representative ancestral sequence that had been derived using bayesian phylogenetic tools. No correlation was seen between peptide-MHC binding affinity and frequency of recognition, as measured by an IFN-γ T cell response in HLA-matched HCV-infected individuals. Peptides encoding representative, consensus, and natural variant sequences were then tested for the capacity to expand CD8 T cell populations and to elicit cross-reactive CD8 T cell responses. CD8(+) T cells expanded with representative sequence HCV generally more broadly and robustly recognized highly diverse circulating HCV strains than did T cells expanded with either consensus sequence or naturally occurring sequence variants. These data support the use of representative sequence in HCV vaccine design.

Hepatitis C virus evasion of adaptive immune responses: a model for viral persistence

Hepatitis C virus (HCV) infects over 170 million people worldwide and is a leading cause of cirrhosis and hepatocellular carcinoma. Approximately 20% [corrected] of those acutely infected clear the infection, whereas the remaining 80% [corrected] progress to chronic infection. Hepatitis C thus provides a model in which successful and unsuccessful responses can be compared to better understand the human response to viral infection. Our laboratory studies the strategies by which HCV evades the adaptive immune response. This review describes the impact of viral mutation on T cell recognition, the role of cell surface inhibitory receptors in recognition of HCV, and the development of antibodies that neutralize HCV infection. Understanding what constitutes an effective immune response in the control of HCV may enable the development of prophylactic and therapeutic vaccines for HCV and other chronic viral infections.

Age at any full-term pregnancy and breast cancer risk

The authors analyzed data from two multistate, population-based case-control studies to investigate the association between age at any full-term pregnancy (FP) and breast cancer risk. Study subjects included breast cancer cases aged 20-79 years identified from four statewide cancer registries and randomly selected controls interviewed from 1988 to 1996. Complete information on a comprehensive set of risk factors for breast cancer was available for 9,891 cases and 12,271 controls. The large number of subjects enabled simultaneous adjustment of the covariates and efficient application of various modeling approaches. Overall, each 5-year increase in age at first FP was associated with an odds ratio of 1.07 (95% confidence interval (CI): 1.01, 1.13) for breast cancer. The corresponding estimates were odds ratio = 1.02 (95% CI: 1.00, 1.05) for age at second through ninth FPs. For age at last FP, the effect estimate (odds ratio = 1.01, 95% CI: 0.97, 1.06) was indistinguishable from that for other FPs after the first. In this analysis, a modest and transient increase in breast cancer risk after childbirth was also observed. The relatively greater effect of age at first FP is consistent with the existence of a long-term effect of early first FP on the differentiation of mammary cells, causing them to become less susceptible to carcinogenesis.

Lactation and a reduced risk of premenopausal breast cancer

BACKGROUND

The evidence of an association of lactation with a reduction in the risk of breast cancer among women has been limited and inconsistent. The effect of lactation appears to be confined to premenopausal women with a history of long lactation, but most studies of this relation have been limited in statistical power. We conducted a multicenter, population-based, case-control study with a sample large enough for us to describe more precisely the association between lactation and the risk of breast cancer.

METHODS

Patients less than 75 years old who had breast cancer were identified from statewide tumor registries in Wisconsin, Massachusetts, Maine, and New Hampshire. Controls were randomly selected from lists of licensed drivers if the case subjects were less than 65 years old, and from lists of Medicare beneficiaries if they were 65 through 74 years old. Information on lactation, reproductive history, and family and medical history was obtained by means of telephone interviews. After the exclusion of nulliparous women, 5878 case subjects and 8216 controls remained for analysis.

RESULTS

After adjustment for parity, age at first delivery, and other risk factors for breast cancer, lactation was associated with a slight reduction in the risk of breast cancer among premenopausal women, as compared with the risk among women who were parous but had never lactated (relative risk, 0.78; 95 percent confidence interval, 0.66 to 0.91); the relative risk of breast cancer among postmenopausal women who had lactated, as compared with those who had not, was 1.04 (95 percent confidence interval, 0.95 to 1.14). With an increasing cumulative duration of lactation, there was a decreasing risk of breast cancer among premenopausal women (P for trend < 0.001) but not among postmenopausal, parous women (P for trend = 0.51). A younger age at first lactation was significantly associated with a reduction in the risk of premenopausal breast cancer (P for trend = 0.003). As compared with parous women who did not lactate, the relative risk of breast cancer among women who first lactated at less than 20 years of age and breast-fed their infants for a total of six months was 0.54 (95 percent confidence interval, 0.36 to 0.82).

CONCLUSIONS

There is a reduction in the risk of breast cancer among premenopausal women who have lactated. No reduction in the risk of breast cancer occurred among postmenopausal women with a history of lactation.