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.