Repetitive peptide boosting progressively enhances functional memory CTLs

Effector functions of memory CTLs can be affected by signals received during reactivation

Memory cytotoxic T lymphocytes (CTLs) are able to provide protections to the host against repeated insults from intracellular pathogens. However, it has not been completely understood how the effector functions of memory CTLs are induced upon antigen challenge, which is directly related to the efficacy of their protection. Third signal cytokines, such as IL-12 and type I interferon, have been suggested to be involved in the protective function of memory CTLs, but direct evidence is warranted. In this report, we found that memory CTLs need to be reactivated to exert effector functions. Infusion of a large population of quiescent memory CTLs did not lead to cancer control in tumor-bearing mice, whereas infusion of a reactivated memory CTL population did. This reactivation of memory CTLs requires cytokines such as IL-12 in addition to antigen but was less dependent upon costimulation and IL-2 compared to naive CTLs. Memory CTLs responded more quickly and with greater strength than their naive counterparts upon stimulation, which is associated with higher upregulation of important transcription factors such as T-bet and phosphorylated STAT4. In addition, memory CTLs underwent less expansion than naive CTLs upon pathogen challenge. In conclusion, effector functions of established memory CTLs may be affected by certain cytokines such as IL-12 and type I IFN. Thus, a pathogen's ability to induce cytokines could contribute to the efficacy of protection of an established memory CTL population.

Boost and loss of immune responses against tumor-associated antigens in the course of pregnancy as a model for allogeneic immunotherapy

Donor-derived immunity against tumor-associated antigens (TAAs) may exert selective antileukemic activity reprieving the allogeneic recipient from graft-versus-host disease. As TAAs are highly expressed in placental tissues we hypothesized that pregnancy could drive respective immunity in healthy individuals. Thus, we investigated the frequency and level of immune responses against clinically relevant TAAs in 114 blood donors and 44 women during their first pregnancy. Quantitative reverse-transcription polymerase chain reaction was employed to detect low levels of interferon-γ after primary peptide stimulation of CD8(+) T lymphocytes. In blood donors, primary immune responses of low and/or high avidity were found against WT1 (15%), MUC1 (14%), PRAME (7%), and HER2/neu (5%) and exerted killing functions against leukemic cells. Men had higher responses than women, likely due to gonadal cancer-testis-antigen expression. Interestingly, a history of prior delivery was not associated with increased responses, whereas the strongest responses during pregnancy were found in early trimesters to disappear after delivery. This boost and loss of TAA-specific immunity suggests that virtually every donor harbors the potential to mount antileukemic immune responses in a recipient. However, in the absence of the driving target and a permissive environment, they are short-lived and thus require supplemental strategies such as vaccination or immunomodulation to facilitate their persistence.

IL-12 is required for mTOR regulation of memory CTLs during viral infection

The induction of functional memory CTLs is a major goal of vaccination against intracellular pathogens. IL-12 is critical for the generation of memory CTLs, and inhibition of mTOR by rapamycin can effectively enhance the memory CTL response. Yet, the role of IL-12 in mTOR’s regulation of memory CTL is unknown. Here, we hypothesized that the immunostimulatory effects of mTOR on memory CTLs requires IL-12 signaling. Our results revealed that rapamycin increased the generation of memory CTLs in vaccinia virus infection, and this enhancement was dependent upon the IL-12 signal. Furthermore, IL-12 receptor deficiency diminished the secondary expansion of rapamycin-regulated memory, and resultant secondary memory CTLs were abolished. Rapamycin enhanced IL-12 signaling by up regulating IL-12 receptor β2 expression and STAT4 phosphorylation in CTLs during early infection. In addition, rapamycin continually suppressed T-bet expression in both WT and IL-12 receptor knockout CTLs. These results indicate an essential role for IL-12 in the regulation of memory CTLs by mTOR, and highlight the importance of considering the interplay between cytokines and adjuvants during vaccine design.

Prospects of combinatorial synthetic peptide vaccine-based immunotherapy against cancer

The insight that the immune system is involved in tumor resistance is gaining momentum and this has led to the development of immunotherapeutic strategies aiming at enhancement of immune-mediated tumor destruction. Although some of these strategies have moderate clinical benefit, most stand-alone therapies fail to significantly affect progressive disease and survival or do so only in a minority of patients. Research on the mechanisms underlying the generation of immune responses against tumors and the immune evasion by tumors has emphasized that various mechanisms simultaneously prevent effective immunity against cancer including inefficient presentation of tumor antigens by dendritic cells and induction of negative immune regulation by regulatory T-cells (Tregs) and myeloid derived suppressor cells (MDSCs). Thus the design of therapies that simultaneously improve effective tumor immunity and counteract immune evasion by tumors seems most desirable for clinical efficacy. As it is unlikely that a single immunotherapeutic strategy addresses all necessary requirements, combinatorial strategies that act synergistically need to be developed. Here we discuss the current knowledge and prospects of treatment with synthetic peptide vaccines that stimulate tumor-specific T-cell responses combined with adjuvants, immune modulating antibodies, cytokines and chemotherapy. We conclude that combinatorial approaches have the best potency to accomplish the most significant tumor destruction but further research is required to optimize such approaches.