Cord blood CD8+ T-cell expansion following granulocyte transfusions eradicates refractory leukemia

Abstract

The action of hematopoietic cell transplantation in controlling leukemia is principally mediated by donor T cells directed against residual recipient malignant cells. However, its utility is limited by graft-versus-host disease (GVHD), where alloreactivity is extended beyond leukemic and marrow cells. In a human/murine chimeric model, we previously showed that the preferential infiltration of cord blood (CB) CD8+ T cells eradicates an Epstein-Barr virus-driven lymphoblastoid tumor without causing xenogeneic GVHD. In the clinic, however, cord blood CD8+ T-cell reconstitution is significantly delayed, and the observation of such a robust antileukemia effect mediated by cord blood CD8+ T cells has not been reported. We describe an observation of very early T-cell expansion in 4 high-risk pediatric leukemia patients receiving third-party, pooled granulocytes after T cell-replete CB transplantation (CBT). The T-cell expansion was transient but robust, including expansion of CD8+ T cells, in contrast to the delayed CD8+ T-cell expansion ordinarily observed after T cell-replete CBT. The CD8+ T cells were polyclonal, rapidly switched to memory phenotype, and had the ability to mediate cytotoxicity. This phenomenon is reproducible, and each patient remains in long-term remission without GVHD. The results suggest that fetal-derived CB CD8+ T cells can be exploited to generate robust antileukemia effects without GVHD.

Conflict of interest statement

Conflict-of-interest disclosure: The authors declare no competing financial interests.

© 2020 by The American Society of Hematology.

Figures

Graphical abstract

Figure 1.

Kinetics of lymphocyte reconstitution in patients 1, 3, 4 and 5. A rapid expansion of T cells was observed very early (between days +7 and +9) after transplantation. It is noteworthy that a very early CD8+ T-cell expansion was observed, in contrast to the significantly delayed CD8+ T-cell reconstitution after typical T cell–replete CBT. ALC, absolute lymphocyte count.

Figure 2.

Magnitude of expansion of T cells in patients 1, 3, 4, and 5. (A) Total number of T cells carried with the CB graft of each index patient was extrapolated from 30 historical CB grafts. Median and IQR of T-cell content from the historical CB grafts were multiplied by weight of the index patient to derive approximate number of T cells transferred at the time of CBT. Total blood volume based on weight of the patient was calculated, and thus, total number of circulating T cells during expansion and magnitude of T-cell proliferation were calculated. Magnitude of T-cell expansion after 168, 192, and 216 hours for each patient is labeled in respective color. (B) Absolute cord blood CD8+ T-cell count in patients 3, 4, and 5 was measured daily during the early unprecedented expansion. CD8+ T-cell expansion is compared with median CD8+ T-cell count (and IQR) of control patients (n = 30) from the historical cohort. (C) Absolute cord blood CD4+ T-cell count in patients 3, 4, and 5 was measured daily during the early expansion. CD4+ T-cell expansion is compared with median CD4+ T-cell count (and IQR) of control patients (n = 30) from the historical cohort.

Figure 3.

Characteristics of preengraftment syndrome in patients with and without granulocyte therapy. (A) Higher levels of CRP were seen in patients who received granulocyte product vs those who did not (P < .001). (B) CRP peaked early in patients who received granulocyte product vs those who did not (P < .0003). (C) Oxygen was required early in patients who received granulocyte product vs those who did not (P < .01). Clinical features such as number of days of fever (D), maximum temperature (E), and number of days of oxygen (F) were not statistically different between 2 groups. NS, not significant.

Figure 4.

TCR spectratyping of CD8+ and CD4+ T cells during T-cell expansion in patient 3.

Figure 5.

CD8+ T-cell differentiation and cytotoxicity in patients with and without granulocyte therapy. (A) Rapid switch from naïve to memory phenotype was observed during expansion of CD8+ T cells in CBT patients receiving granulocytes (n = 2; patients 3 and 4). In contrast, only 6% to 27% of CB CD8+ T cells switched to memory phenotype at 30 days after transplantation in those not receiving granulocytes. (B) CD8+ T cells during early expansion acquired cytotoxic function (CD107a) on anti-CD3 stimulation. CD107a was significantly higher in index patients compared with the adult control. In contrast, a patient who underwent CBT without granulocyte transfusion had (low) CD107a, similar to the control.