SI12 Lymphocyte Subsets Following Autologous Transfer of CD25 Depleted Leukapheresis Products

A subset of T lymphocytes known as regulatory T-cells (Tregs) plays a pivotal role in suppressing the immune system in particular the function of effector T-cells. Tregs have been identified by the cell surface co-expression of CD4 and high levels of CD25 (IL-2 receptor α chain) together with CD45RO, CTLA-4, GITR and the nuclear transcription factor foxp3. Cancer patients with advanced malignancies (renal, gastric etc.) have high numbers of circulating Tregs compared to healthy controls. Experiments in mice indicate a role for Tregs in controlling immune rejection of tumours. In particular, adoptive transfer of CD25+ depleted T-cell populations induces potent responses to syngeneic tumours. Adoptive transfer of CD25+ depleted autologous Tcells is therefore a potential anti-cancer treatment. We have begun a study in which autologous leukapheresis products are depleted of CD25+ cells using CD25 CliniMACS® reagent and the CliniMACS® System. The CD25+ depleted product is transferred back to the patient following nonmyeloablative chemotherapy to deplete the host T-cell repertoire. We report here on the changes to the cellular immune repertoire (CD45, CD3, CD4, CD8, CD19 and CD56) in the first three patients receiving this treatment. In all three cases, the CliniMACS® process gave >2 log depletion of CD25+ lymphocytes. The number of CD3+ cells received were 1.3, 0.6 and 0.9 × 107 kg−1 for patient 1, 2 and 3 respectively. At the time of cell receipt all three patients had CD3 counts of <5 μL−1, rising in patients one and three to above 200 μL−1 by days 9 and 10 respectively, with patient two taking 14–21 days to reach a similar level. The CD4 : 8 ratios were 2.3 and 2.8 (patient 1 and 2, day 7) and 7.3 (patient 3, day 8) dropping to 0.1–0.2 between 14 and 21 days. On day 21 the CD4 : 8 ratio for patient one rose to 1.7 associated with an allergic reaction to prophylactic antibiotic. By day 77 the CD4 : 8 ratios were 0.8 for patient one, and 0.4 for patients two and three. B cell numbers showed signs of recovery in all three patients by day 42. NK cells reached 250–300 μL−1 by days 14–21 but dropped to around 100 μL−1 by day 77 in all three patients. The lymphocyte subset data thus far do not indicate any untoward reactions to the chemotherapy or the depletion of the CD25+ lymphocyte population from the transferred cells.