Adaptive immunity cooperates with liposomalall-trans-retinoic acid (ATRA) to facilitate long-term molecular remissions in mice with acute promyelocytic leukemia

Abstract

We previously developed a murine model of acute promyelocytic leukemia (APL) by using human cathepsin G gene regulatory elements to direct the expression of promyelocytic leukemia (PML)͞retinoic acid receptor ␣ (RAR␣) and RAR␣͞PML fusion cDNAs to the early myeloid compartment of transgenic mice. To study the efficacy of noncytotoxic therapy in this animal model, cohorts of naive immunocompetent mice were inoculated with primary murine APL cells from a frozen tumor bank. Arsenic trioxide and liposomally encapsulated all-trans-retinoic acid (Lipo ATRA), alone or in combination, were administered for 21 days by i.p. injection using doses that yielded plasma levels similar to those observed in human APL patients treated with these agents. Lipo ATRA was highly effective in inducing durable molecular remissions in immunocompetent mice [C57BL͞6 ؋ C3H F 1 (B6C3HF1)]; arsenic therapy was much less effective, and did not clearly synergize with Lipo ATRA to increase the remission rate in immunocompetent mice. The survival of Lipo ATRA-treated severe combined immunodeficient (SCID) animals (lacking functional T and B cells) was inferior to that of immunocompetent B6C3HF1 recipients (40% vs. 88% survival at 1 y, P < 0.001). These data suggest that adaptive immunity cooperates with pharmacologic therapy to induce or maintain remissions in murine APL. It also implies that immunosuppressive anti-leukemia therapies could paradoxically blunt effective anti-leukemia immune responses that are important for clearing small numbers of residual tumor cells after chemotherapy-mediated cytoreduction.A cute promyelocytic leukemia (APL) is usually associated with a t(15;17)(q22;q11.2-12) balanced translocation that creates in-frame fusions between the gene encoding the promyelocytic leukemia (PML) gene on chromosome 15 and retinoic acid receptor ␣ (RAR␣) gene on chromosome 17 (1). We and others have demonstrated that the expression of PML͞RAR␣ in the early myeloid compartment of transgenic mice is necessary but not sufficient for the development of APL (2-4). We have also shown that coexpression of a reciprocal RAR␣͞PML cDNA together with PML͞RAR␣ substantially increases the likelihood of APL development (5, 6).The incorporation of all-trans-retinoic acid (ATRA) into the standard treatment regimens for APL has rendered it the most curable of the AML subtypes. Despite remission rates of up to 90% with oral ATRA alone, this therapy usually does not generate molecular remissions, and must be combined with cytotoxic chemotherapy to effect cures (7). However, recent studies have shown that liposomally encapsulated ATRA (Lipo ATRA), when given to patients as a single agent (''monotherapy''), can directly induce molecular remissions in APL patients (8-10). The role of chemotherapy to consolidate remissions induced by Lipo ATRA is not yet clear.In this report, we evaluate the effectiveness of ATRA and arsenic trioxide in a well-characterized mouse model of APL.We define treatment protocols that yield drug levels of ATRA and arsenic that are very s...

Rara haploinsufficiency modestly influences the phenotype of acute promyelocytic leukemia in mice

“…Five days later, engraftment was confirmed by flow cytometry of peripheral blood (peridinin chlorophyll A protein [PerCP]-Cy5.5-␣CD45.2; eBioscience 104), and mice were treated with ATRA (10 mg, 21-day sustained-release pellets, Innovative Research of America), as described previously. 34 The Washington University Animal Studies Committee approved all animal experiments.…”

“…Similar to our prior observations, there was heterogeneity in the latency (6-12 weeks), but very little variability between replicate recipients. 34 After confirming engraftment of CD45.2 ϩ /Gr1 ϩ peripheral blood cells 5 days after transplant, half of each replicate cohort was treated with sustainedrelease ATRA pellets. ATRA led to decreased numbers of CD45.2 ϩ peripheral blood cells, evidence of leukemic differentiation with an immunophenotypic shift of CD45.2 ϩ peripheral blood cells from Gr1 ϩ /cKit ϩ /CD11b low to Gr1 ϩ /cKit Ϫ /CD11b high , and improved survival regardless of Rara status (data not shown).…”

Leukocyte Homing, Fate, and Function Are Controlled by Retinoic Acid

“…Other studies found that in both tumor-bearing mice (102) and cancer patients (220), high-dose RA treatment can induce the differentiation of immature myeloid-derived suppressor cells (MDSC) into mature DCs, thus diminishing the tolerance of T cells and generating greater T-cell responses against the tumor. An earlier study showed that liposomal RA treatment induced regression of murine acute promyelocytic leukemia in cooperation with adaptive immunity (210). In line with these findings, combination of a DNA vaccine and RA administration induced robust CD4 ϩ and CD8 ϩ T-cell immunity and enabled long-term survival in an acute promyelocytic leukemia mouse model, although ATRA alone failed to elicit pronounced T-cell immunity (56).…”

Effects of arsenite on macropinocytotic and autophagic activities in CHO-K1 cells

“…The plasma level of arsenic in the clinical management of acute promyelocytic leukemia usually reaches 5.5-7.3 mM [30]. It has been reported that the peak concentration of plasma arsenic level was 10.6 mM after intraperitoneal administration of 0.2 mg (10 mg/kg) of ATO in mice [31]. The dosage used in our current study was 6 mg/kg ATO in mice represent a concentration of plasma arsenic level of 6.4 mM, which is clinically relevant.…”