Biological Characteristics of T Cells from CD4 Idiopathic Lymphocytopenia Patients Activated and Expanded Using Xcellerate™ Technology.

Idiopathic CD4 lymphocytopenia (ICL) is characterized by reduced CD4⁺ T cell counts in the absence of HIV infection or other defined causes. Patients with ICL generally have CD4⁺ T cell counts < 100/μL and are at risk for infections. Administration of IL-2 has been reported to reduce the risk of infections in some patients, but CD4⁺ T cell counts remain low. Currently, there is no available therapy to increase the number of CD4⁺ T cells in these patients.

We have developed the Xcellerate™ Technology, in which T cells are activated and expanded ex vivo from peripheral blood mononuclear cells (PBMC) using microscopic paramagnetic beads conjugated with anti-CD3 and anti-CD28 monoclonal antibodies (Xcyte™Dynabeads®). In patients with low CD4 counts due to HIV or cancer chemotherapy, administration of T cells activated and expanded using the Xcellerate Technology or similar process leads to significant increases in CD4⁺ T cell counts to normal levels that are sustained over several months.

In the current study, we tested the ability of the Xcellerate Technology to expand T cells from patients with ICL. We collected data on T cell phenotype, cell expansion, activation marker expression, cytokine secretion, T cell receptor (TCR) repertoire diversity, functional potential and response to restimulation. T cells expanded a median of 902 fold (range 281–1529; n=3 patients), and demonstrated typical induction of surface-activation marker expression, including upregulation of CD25 (IL-2R) and CD154 (CD40L). Phenotypic compositions of the ICL donor PBMC were heterogenous both before and after T cell expansion. Two patients had very high levels of CD4⁻CD8⁻ T cells, and one of these two patients also had very high levels of γδ⁺ T cells. Each of these populations was maintained throughout expansion. The other patient displayed high levels of circulating CD3⁺CD56⁺ NKT cells that did not proliferate as robustly as other T cells during the expansion process. For two patients, flow cytometric analysis revealed a normal pattern of TCR Vβ surface expression while the remaining tissue had a skewed TCR Vβ distribution pattern. Following initial expansion and subsequent restimulation, T cells rapidly re-expressed surface activation markers and cytokines. In these preliminary studies, T cells from patients with ICL were expanded successfully using the Xcellerate Technology, suggesting that this approach might be used for clinical application in this disease.

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