Immune reconstitution in recipients of photodepleted HLA-identical sibling donor stem cell transplantations: T cell subset frequencies predict outcome

Abstract

We evaluated an ex vivo photodepletion (PD) technique to selectively deplete graft-versus-host disease (GVHD) alloreacting T cells given to 24 human leukocyte antigen (HLA)-identical sibling stem cell transplantation (SCT) recipients. Donor lymphocytes were activated by 72-hour exposure to irradiated in vitro expanded recipient T lymphocytes and pulsed with a TH9402 photosensitizer. Alloactivated T cells preferentially retaining the photosensitizer were eliminated by light exposure. The PD product showed an inverted CD4(+)/CD8(+) ratio with greatest depletion occurring in the CD4(+) naive and central memory populations. In contrast, the CD8(+) naive and effector cells were relatively conserved, reflecting the differential extrusion of TH9402 by T cell subsets. Cytomegalovirus reactive T cells were reduced in the PD product and in recipient blood 100 days after SCT when compared with contemporaneous HLA-identical sibling donor T cell-depleted SCT recipients. Although PD SCT recipients experienced similar absolute lymphocyte counts during the first 100 days after SCT, they achieved 100% donor T cell chimerism more rapidly and had higher CD8(+) naive T cell counts early after SCT. SCT recipients of PD products with the lowest CD4 central memory content had the highest risk of developing chronic GVHD (cGVHD) (P = .04) and a poorer survival (P = .03). Although the persistence of CD8(+) naive T cells may have contributed to important antileukemia responses resulting in a relatively low relapse rate, our findings emphasize the role of donor memory T cells and CD4 cells in establishing immune competence post-SCT. Although PD is associated with excellent outcomes in the haploidentical setting, the low frequency of alloactivations in HLA-matched pairs makes the PD approach used by our group for allodepletion in HLA-matched sibling transplantations an inefficient technique.

Figure 1

Changes in frequency of T cell subsets after PD. Mean percentage +/− SEM of the A) CD4, B) the CD8 T cell subsets, C) Tregs, and D) NK and B cells before (solid bar) and after PD (white bar). EM, effector memory; CM, central memory.

Figure 2

Differences in TH9402 extrusion of T cell subsets in representative sample by flow cytometry.

Figure 3

T cell proliferation against CMV antigens before and after PD.

Figure 4

A) Absolute lymphocyte counts during the first 100 days for patient receiving either a T cell depleted (open circles) or photodepleted (dark squares) SCT. B) T cell chimerism during the first 100 days after SCT.

Figure 5

Ex vivo anti-CMV immune response in samples collected 100 days after PD and TCD SCT in the A) CD4 and B) CD8 T cells. PD, photodepletion; TCD, T cell depletion; TNF, tumor necrosis factor.

Figure 6

Overall survival of patients receiving a PD SCT. Median frequency of CD4 central memory cells of 15% was used for survival curve generation (Logrank HR 7.7, p = 0.006). PD, photodepletion; CM, central memory.