Adaptive immune responses are defined as antigen-sensitization-dependent and antigen-specific responses leading to establishment of long-lived immunological memory. While natural killer (NK) cells have traditionally been considered cells of the innate immune system, mounting evidence in mice and non-human primates warrants reconsideration of the existing paradigm that B and T cells are the sole mediators of adaptive immunity. However, it is currently unknown whether human NK cells can exhibit adaptive immune responses. We therefore tested whether human NK cells mediate adaptive immunity to virally encoded antigens using humanized mice and human volunteers. We found that human NK cells displayed vaccination-dependent, antigen-specific recall responses in vitro, when isolated from livers of humanized mice previously vaccinated with human immunodeficiency virus (HIV)-encoded envelope protein. Furthermore, we discovered that large numbers of cytotoxic NK cells with a tissue-resident phenotype were recruited to sites of varicella-zoster virus (VZV) skin test antigen challenge in VZV-experienced human volunteers. These NK-mediated recall responses in humans occurred decades after initial VZV exposure, demonstrating that NK memory in humans is long-lived. Our data demonstrates that human NK cells exhibit adaptive immune responses upon vaccination or infection. The existence of human memory NK cells may allow for the development of vaccination-based approaches capable of establishing potent NK-mediated memory functions contributing to host protection.

HIV infection is associated with a much higher risk for the development of non-Hodgkin lymphoma (AIDS-NHL). The principal causes of lymphomagenesis in HIV-infected individuals are thought to be the loss of immune function seen in HIV infection, which results in the loss of immunoregulation of Epstein–Barr virus-infected B cells, as well as HIV infection-associated immune dysregulation, including chronic B-cell activation. In this review, we discuss recent reports that further support the importance of these factors, and we highlight emerging evidence of different mechanisms that potentially drive lymphomagenesis in HIV-infected individuals.

Background: HIV infection is associated with a marked increase in risk for non-Hodgkin lymphoma (AIDS-NHL). However, the mechanisms that promote the development of AIDS-NHL are not fully understood. Methods: In this study serum levels of several cytokines and other molecules associated with immune activation were measured in specimens collected longitudinally during 1-to-5 years preceding AIDS-NHL diagnosis, in 176 AIDS-NHL cases and 176 HIV+ controls from the Multicenter AIDS Cohort Study (MACS). Results: Multivariate analyses revealed that serum levels of immunoglobulin free light chains (FLC), IL-6, IL-10, IP-10/CXCL10, neopterin, and TNFα were elevated in those HIV+ individuals who went on to develop AIDS-NHL. Additionally, the fraction of specimens with detectable IL-2 was increased, and the fraction with detectable IL-4 was decreased, in these subjects. Conclusions: These results suggest that long term, chronic immune activation, possibly driven by macrophage-produced cytokines, precedes development of NHL in HIV+ individuals. Impact: FLC, IL-6, IL-10, IP-10/CXCL10, neopterin, and TNFα may serve as biomarkers for AIDS-NHL.

A novel homozygous mutation in human IL2RB results in decreased IL-2Rβ protein expression and dysregulated IL-2/15 signaling. This hypomorphic mutation leads to decreased regulatory T cell frequency and an abnormal NK cell compartment, with clinical manifestations of autoimmunity and susceptibility to CMV.

Objective: Our objective was to investigate the mechanisms that govern natural killer (NK)-cell responses to HIV, with a focus on specific receptor--ligand interactions involved in HIV recognition by NK cells. Design and Methods: We first performed a mass cytometry-based screen of NK-cell receptor expression patterns in healthy controls and HIV+ individuals. We then focused mechanistic studies on the expression and function of T cell immunoreceptor with Ig and ITIM domains (TIGIT). Results: The mass cytometry screen revealed that TIGIT is upregulated on NK cells of untreated HIV+ women, but not in antiretroviral-treated women. TIGIT is an inhibitory receptor that is thought to mark exhausted NK cells; however, blocking TIGIT did not improve anti-HIV NK-cell responses. In fact, the TIGIT ligands CD112 and CD155 were not upregulated on CD4+ T cells in vitro or in vivo, providing an explanation for the lack of benefit from TIGIT blockade. TIGIT expression marked a unique subset of NK cells that express significantly higher levels of NK-cell-activating receptors (DNAM-1, NTB-A, 2B4, CD2) and exhibit a mature/adaptive phenotype (CD57hi, NKG2Chi, LILRB1hi, FcRγlo, Syklo). Furthermore, TIGIT+ NK cells had increased responses to mock-infected and HIV-infected autologous CD4+ T cells, and to PMA/ionomycin, cytokine stimulation and the K562 cancer cell line. Conclusion: TIGIT expression is increased on NK cells from untreated HIV+ individuals. Although TIGIT does not participate directly to the response to HIV-infected cells, it marks a population of mature/adaptive NK cells with increased functional responses.

The DNA-modifying processes that are involved in B lymphocyte activation, somatic hypermutation (SHM) and IgH class switch recombination (CSR), have the potential to lead to genetic errors that lead to the genesis of B cell cancers, such as lymphoma. Given the potential contribution of these immune mechanisms to the development of cancer, assessment of the expression of cytokines and other immune stimulatory molecules that drive B cell activation, prior to lymphoma diagnosis, may provide insights into the etiology of these cancers. Here, we review studies that have examined pre-diagnosis protein biomarkers for non-Hodgkin lymphoma (NHL), both AIDS-related NHL, as well as NHL seen in immunocompetent populations. Overall, these studies provide support for the notion that B cell hyper-activation is elevated preceding the appearance of AIDS-NHL, particularly those forms of AIDS-NHL that are not driven by EBV infection, and which presumably arise from errors in IgH CSR and SHM. In more limited studies, it appears that dysregulation of cytokine production also precedes the diagnosis of NHL in HIV-negative persons. The availability of pre-diagnosis serum/plasma from cohort studies provides unique opportunities for proteomic approaches to identify novel pre-diagnosis etiologic biomarkers for NHL.

Background Natural killer (NK) cells have antiviral and antitumor activity that could be harnessed for the treatment of infections and malignancies. To maintain cell viability and enhance antiviral and antitumor effects, NK cells are frequently treated with cytokines. Here we performed an extensive assessment of the effects of cytokines on the phenotype and function of human NK cells. Methods We used cytometry by time-of-flight (CyTOF) to evaluate NK cell repertoire changes after stimulation with interleukin (IL)-2, IL-15 or a combination of IL-12/IL-15/IL-18. To analyze the high dimensional CyTOF data, we used several statistical and visualization tools, including viSNE (Visualization of t-Distributed Stochastic Neighbor Embedding), Citrus (Cluster identification, characterization, and regression), correspondence analysis, and the Friedman-Rafsky test. Results All three treatments (IL-2, IL-15, and IL-12/IL-15/IL-18) increase expression of CD56 and CD69. The effects of treatment with IL-2 and IL-15 are nearly indistinguishable and characterized principally by increased expression of surface markers including CD56, NKp30, NKp44, and increased expression of functional markers, such as perforin, granzyme B, and MIP-1β. The combination of IL-12/IL-15/IL-18 induces a profound shift in the repertoire structure, decreasing expression of CD16, CD57, CD8, NKp30, NKp46, and NKG2D, and dramatically increasing expression of IFN-γ. Conclusions CyTOF provides insights into the effects of cytokines on the phenotype and function of NK cells, which could inform future research efforts and approaches to NK cell immunotherapy. There are several analytical approaches to CyTOF data, and the appropriate method should be carefully selected based on which aspect of the dataset is being explored.

Background CXCL13 and CXCR5 are a chemokine and receptor pair whose interaction is critical for naïve B cell trafficking and activation within germinal centers. We sought to determine whether CXCL13 levels are elevated prior to HIV-associated non-Hodgkin B-cell lymphoma (AIDS-NHL), and whether polymorphisms in CXCL13 or CXCR5 are associated with AIDS-NHL risk and CXCL13 levels in a large cohort of HIV-infected men. Methods CXCL13 levels were measured in sera from 179 AIDS-NHL cases and 179 controls at three time-points. TagSNPs in CXCL13 (n=16) and CXCR5 (n=11) were genotyped in 183 AIDS-NHL cases and 533 controls. Odds ratios (OR) and 95% confidence intervals (CIs) for the associations between one unit increase in log CXCL13 levels and AIDS-NHL, as well as tagSNP genotypes and AIDS-NHL, were computed using logistic regression. Mixed linear regression was used to estimate mean ratios (MR) for the association between tagSNPs and CXCL13 levels. Results CXCL13 levels were elevated >3 years (OR=3.24, 95% CI=1.90–5.54), 1–3 years (OR=3.39, 95% CI=1.94–5.94) and 0–1 year (OR=3.94, 95% CI=1.98–7.81) prior to an AIDS-NHL diagnosis. The minor allele of CXCL13 rs355689 was associated with reduced AIDS-NHL risk (ORTCvsTT=0.65; 95% CI=0.45–0.96) and reduced CXCL13 levels (MRCCvsTT=0.82, 95% CI=0.68–0.99). The minor allele of CXCR5 rs630923 was associated with increased CXCL13 levels (MRAAvsTT=2.40, 95% CI=1.43–4.50). Conclusions CXCL13 levels were elevated preceding an AIDS-NHL diagnosis, genetic variation in CXCL13 may contribute to AIDS-NHL risk, and CXCL13 levels may be associated with genetic variation in CXCL13 and CXCR5. Impact CXCL13 may serve as a biomarker for early AIDS-NHL detection.