IL-2 intratumoral immunotherapy enhances CD8+ T cells that mediate destruction of tumor cells and tumor-associated vasculature: a novel mechanism for IL-2

Therapeutic use of IL-2 can generate antitumor immunity; however, a variety of different mechanisms have been reported. We injected IL-2 intratumorally (i.t.) at different stages of growth, using our unique murine model of mesothelioma (AE17; and AE17 transfected with secretory OVA (AE17-sOVA)), and systematically analyzed real-time events as they occurred in vivo. The majority of mice with small tumors when treatment commenced displayed complete tumor regression, remained tumor free for >2 mo, and survived rechallenge with AE17 tumor cells. However, mice with large tumors at the start of treatment failed to respond. Timing experiments showed that IL-2-mediated responses were dependent upon tumor size, not on the duration of disease. Although i.t. IL-2 did not alter tumor Ag presentation in draining lymph nodes, it did enhance a previously primed, endogenous, tumor-specific in vivo CTL response that coincided with regressing tumors. Both CD4(+) and CD8(+) cells were required for IL-2-mediated tumor eradication, because IL-2 therapy failed in CD4(+)-depleted, CD8(+)-depleted, and both CD4(+)- and CD8(+)-depleted C57BL/6J animals. Tumor-infiltrating CD8(+) T cells, but not CD4(+) T cells, increased in association with a marked reduction in tumor-associated vascularity. Destruction of blood vessels required CD8(+) T cells, because this did not occur in nude mice or in CD8(+)-depleted C57BL/6J mice. These results show that repeated doses of i.t. (but not systemic) IL-2 mediates tumor regression via an enhanced endogenous tumor-specific CTL response concomitant with reduced vasculature, thereby demonstrating a novel mechanism for IL-2 activity.     

Immunity,antigenic heterogeneity,and aggregation of helminth parasites

Empirical studies of helminth parasites reveal that the distribution of parasite burdens in their host populations is highly aggregated. This aggregation is fundamental to the ecology and epidemiology of helminth parasites. Results from a stochastic model predict that aggregation of helminth parasites is inversely related to the intensity of host immunity. Aggregation also decreases with antigenic heterogeneity and increases with heterogeneity in transmissibility among parasite strains. It is also found that the degree of aggregation is greater when immunity affects parasite fecundity than when immunity acts on host susceptibility. Potential relevance of this result for assessing the influence of vaccines that target either host susceptibility or parasite fecundity on the level of aggregation and consequent effects on drug resistance and disease prevalence are discussed.     

Diminished proliferation of human immunodeficiency virus-specific CD4+ T cells is associated with diminished interleukin-2 (IL-2) production and is recovered by exogenous IL-2

Virus-specific CD4(+) T-cell function is thought to play a central role in induction and maintenance of effective CD8(+) T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4(+) T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4(+) T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-gamma in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer(+) or total-Gag-specific CD4(+) T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4(+) T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4(+) T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously.     

Hepatitis delta virus RNA encoding the large delta antigen cannot sustain replication due to rapid accumulation of mutations associated with RNA editing

Hepatitis delta virus (HDV) contains two RNA species (HDV-S and HDV-L), which encode the small and large forms of hepatitis delta antigens (S- and L-HDAg), respectively. HDV-L RNA is a result of an RNA editing event occurring at an amber/W site of HDV-S RNA. RNA editing must be regulated to prevent premature and excessive accumulation of HDV-L RNA in the viral life cycle. In this study, we used an RNA transfection procedure to study the replication abilities of HDV-L and HDV-S RNA. While HDV-S led to robust RNA replication, HDV-L could not replicate even after 6 days following transfection. The failure of HDV-L to replicate was not due to insufficient amounts of S-HDAg, as identical results were obtained in a cell line that stably overexpresses S-HDAg. Also, it was not due to possible inhibition by L-HDAg, as HDV-S RNA replication was not affected when both HDV-L and HDV-S RNA were cotransfected. Further, when L-HDAg expression from HDV-L RNA was abolished by site-directed mutagenesis, the mutant HDV-L RNA also failed to replicate. Unexpectedly, when the kinetics of RNA replication was examined daily, HDV-L was found to replicate at a low level at the early time points (1 to 2 days posttransfection) but then lose this capability at later time points. Sequence analysis of the replicated HDV-L RNA at day 1 posttransfection showed that it had undergone multiple nucleotide changes, particularly in the region near the putative promoter region of HDV RNA replication. In contrast, very few mutations were found in HDV-S RNA. These results suggest that the editing at the amber/W site triggers a series of additional mutations which rapidly reduce the replication efficiency of the resultant HDV genome and thus help regulate the amount of HDV-L RNA in infected cells. They also explain why L-HDAg is not produced early in HDV infection, despite the fact that HDV-L RNA is present in the virion.     

Identification and simian immunodeficiency virus infection of CD1d-restricted macaque natural killer T cells

Natural killer T (NKT) cells express a highly conserved T-cell receptor (TCR) and recognize glycolipids in the context of CD1d molecules. We recently demonstrated that CD4+ NKT cells are highly susceptible to human immunodeficiency virus type 1 (HIV-1) infection and are selectively depleted in HIV-infected individuals. Here, we identified macaque NKT cells using CD1d tetramers and human Valpha24 antibodies. Similar to human NKT cells, alpha-galactosylceramide (alpha-GalCer)-pulsed dendritic cells activate and expand macaque NKT cells. Upon restimulation with alpha-GalCer-pulsed CD1d(+) cells, macaque NKT cells secreted high levels of cytokines, a characteristic of these T cells. Remarkably, the majority of resting and activated macaque NKT cells expressed CD8, and a smaller portion expressed CD4. Macaque NKT cells also expressed the HIV-1/simian immunodeficiency virus (SIV) coreceptor CCR5, and the CD4+ subset was susceptible to SIV infection. Identification of macaque NKT cells has major implications for delineating the role of these cells in nonhuman primate disease models of HIV as well as other pathological conditions, such as allograft rejection and autoimmunity.