A decade of CD4+ chimeric antigen receptor T-cell evolution in two chronic lymphocytic leukemia patients: were chronic lymphocytic leukemia cells present?

Abstract

On Feb 2, 2022, Nature published the paper titled "Decade-long leukemia remissions with the persistence of CD4+ CAR T-cells" (Nature. 2022;602:503-9. doi: 10.1038/s41586-021-04390-6). According to the results presented, it could be argued that "chimeric antigen receptor (CAR) T-cells can actually cure patients with chronic lymphocytic leukemia (CLL)". CAR T-cells remained detectable more than ten years after infusion, and immunoglobulin heavy chain (IGH) rearrangement deep sequencing showed persistent deep molecular remission for both patients (no CLL clonotypes were detectable six months after CAR T-cell infusion and onwards). However, the existing actual disease status of both patients remained unclear, as it was unknown: (1) if CAR T-cells killed all leukemia cells during the initial anti-leukemic response phase, that is, soon after CAR T-cell infusion into both patients; (2) if few CLL cells survived, but persistent CAR T-cells had been able to destroy any leukemia cells before they reach detectable levels. In the first case, both patients could be considered definitely cured; in the second not and their decade-prolonged deep remission could be a consequence of the cytotoxic activity of the functionally active CD4+ CAR T-cells. The first version appears to be stronger and the supporting arguments have been included in a comprehensive commentary article. A new therapeutic intervention may emerge with the potential to fully improve the quality of life of both patients and in addition, ongoing research into CAR T-cells may turn in a new, more effective direction.

Keywords: CD4+/CD8+ T-lymphocytes; Chimeric antigen receptor T-cells; chronic lymphocytic leukemia; immunotherapy; long-term remission.

Figure 1

Temporal analysis of cell composition in two CLL patients. A. Cytotoxic CD8+ CAR T-cells expanded and dominated in the initial response phase mediating the killing of CLL cells, which remained undetected six months after CAR T-cell infusion. CD8+ CAR T-cells gradually declined and shifted to CD4+ CAR T-cells, which dominated at low levels over the second phase. In parallel, normal CD19+ B-cells gradually declined resulting in B-cell aplasia, while in the first patient B-cells gradually restored at 8 years post CAR T-cell infusion without disease recurrence. The actual CLL cell status remained unclear after six months, namely, whether the CLL burden was completely eradicated during the initial phase or some residual CLL cells remained over a decade and were destroyed by very few patrol-activated CD4+ CAR T-cells; B. temporal analysis of cell composition in two CLL patients. Estimation of the mean percentage of persisting CAR T-cells out of overall T-cells over two distinct phases in two CLL patients (based on Figure 1b, c [7] and Figure 2a [1], Figure 1b, c is a figure of [7], Figure 2a is a figure of [1], not this article). During the first six months post CAR T-cell infusion, the mean percentage of CAR T-cells out of all T-cells was approximately 35% in patient 1 and approximately 25% in patient 2. The corresponding percentages in the second phase were 0.217% in patient 1 and 1.266% in patient 2

Figure 2

Recommendations for future research and clinical applications in the CAR T-cell field. A. CAR T-cells should be administered in high doses and in a split-dosing manner for safety reasons; B. research should shift to detect tumor-specific antigens and invent more sensitive techniques to facilitate the interpretation of results; C. the CAR T-cell starting material should be defined in terms of composition of CAR T-cell subpopulations; D. anti-idiotypic antibodies should be developed and administered in potentially “cured” CLL patients who are under high risk of infections, to eradicate remaining CAR T-cells and restore B-cell aplasia; E. remission or cure? larger cohorts are needed to confirm the clinical status across other CLL patients, as well as other malignancies