Is it necessary to deplete the lymphokine activated killers’ populations of CD4+CD25+ lymphocytes? Regulatory Foxp3-positive T cells within lymphokine activated killers

LAKs are used in cancer therapy. A common argument against LAK therapy is the probability of the activation of Tregs by IL-2 alongside with NK cells. In order to evaluate negative impact of Tregs, contents of Foxp3+CD4+CD25+ Tregs and their influence on LAKs’ cytotoxic activity in the samples of healthy volunteers’ PBMCs cultured with or without IL-2 were determined. A marked increase in the proportion of the CD4+CD25+ T cells in the most of the PBMCs cultured with IL-2 was evident. Surprisingly, the contents of Foxp3+CD4+CD25+ Tregs showed variable response to IL-2 in blood samples of different people. Their proportions increased, remained on the same level or even decreased compared to PBMCs cultured without exogenous IL-2. Different methods of Treg isolation were compared regarding the purities of the resulting T-cell populations and their enrichment in the Foxp3-expressing Tregs, as well as their viability. Neither of the kits applied provided any enrichment in Foxp3-level in the purified cells compared to the CD4+CD25+ T cells gated on applying flow-cytometric cell analysis in the non-separated LAKs. Moreover, the addition of the purified supposedly Tregs to LAKs never inhibited their cytotoxic reactions, even then they were added in great non-physiological excess. In some of the blood samples, there have been detected another non-identified type of the Foxp3-expressing cells, which lacked CD25, as well as CD4. They may be a new type of regulatory cells, which has not been described before.