Concurrent Treatment with Denileukin Diftitox (DD) To Deplete T-Regulatory Cells Enhances Rebound Lymphocytosis and Eosinophilia in Patients Treated with High-Dose IL-2 (HDIL-2) for Metastatic Renal Cell Cancer (MRCC).

Background: CD4⁺CD25⁺hi T cells (T_reg) play a suppressive role in immune regulation. DD is an IL-2 receptor specific cytotoxin. We postulated depletion of T_reg with DD may enhance immune effector cell populations after HDIL-2 treatment, including rebound lymphocytosis and also eosinophilia which has been reported to be involved in immune response to neoplasm (Mattes J Exp Med 197: 387, 2003).

Methods: In this pilot study, 12 pts (8 male, median age 58 yrs) with MRCC were tx with HDIL-2 and DD in different schedules to determine safety and effect on immune response as manifested by changes in T_reg, peak lymphocyte, and eosinophil counts. Pts were treated with IL-2 600,000 IU/kg Q8H on days (d) 1–5 and 15–19. Three (group A) and 4 (group B) pts were given 6 and 9ug/kg daily on d8–10 respectively, while 5 (group C) pts received 9ug/kg of DD on d −4 to −2. Nine (group D) pts with metastatic melanoma who received HDIL-2 as above but without DD were included as controls. Flow cytometry was done on days −4, 1,8,10,15,22 for group C and on days 1,8,10,15,22 for groups B, and D. CBC was obtained concurrent or within 24 hours of flow cytometry. Group A pts were evaluated for safety only and were excluded from analysis.

Results: Prior to enrollment, all pts had undergone nephrectomy and four patients received interferon-alpha. One pt from group B withdrew from study and was not included in analysis. Administration of DD resulted in a median decline of 25% in T_reg number (not significant). DD given before HDIL-2 was associated with a greater increase in T_reg post HDIL-2. In Group C there was an increase of rebound median T_reg count of 0.88k/ul compared with 0.060k/ul in group B (p=0.025). Absolute lymphocytosis was higher in the combined group getting DD compared to control (median maximal increase of 7.6 vs 4.7 k/ul, respectively) although the difference did not reach statistical significance. However, group C pts had a greater increase in absolute lymphocytosis than did group B pts in which absolute lymphocytosis actually decreased (median increase 10.6 vs. median decrease 0.4 k/ul, p=0.025). A higher peak level of eosinophilia was noted in groups B and C compared with group D (mean increase of 10.5 vs. 4.0 k/ul p=0.2). Group C had a greater peak eosinophilia than group B (11.2 vs 2.2 k/ul p=0.053) Toxicity was manageable and consistent with those seen with HDIL-2. Median HDIL-2 dose given was 21 (range, 14–28). No clinical responses were observed. Of 11 pts included in the analysis 1 pt from group A expired 68 weeks after enrollment. All remaining patients are alive. Survival from enrollment ranges from 11 to 93 weeks.

Conclusion: Overall, the combination of DD and HDIL-2 results in a stimulatory effect as manifested by increased rebound lymphocytosis and eosinophilia compared to HDIL-2 alone. Administration of DD in conjunction with HDIL-2 was associated with a rebound in T_reg that may be schedule and dose dependent. The results suggest an enhanced immune stimulatory effect as manifested by lymphocytosis and peak eosinophilia in group C. However, this stimulatory effect also extends to T_reg that may prove detrimental clinically. Further exploration of these effects in immunotherapy naïve patients would be beneficial.