Immunological Derangement in Follicular Lymphoma Patients Developing Severe Side Effects during Treatment with PI3K Inhibitors

Introduction

Phosphoinositide-3-kinases (PI3Ks) are pivotal in various cellular functions including proliferation and survival, cell differentiation, intracellular trafficking and immunity. The PI3Kδ isoform is highly expressed in cells of hematopoietic origin, and is often dysregulated in various hematologic malignancies. 

New drugs targeting PI3Ks have emerged as promising treatment options for patients (pts) with CLL and indolent NHL, but a clear understanding of their effects on pts' immunity is lacking. Herein we performed detailed immunological analysis in two follicular lymphoma (FL) pts treated with PI3K inhibitors and developing severe immune-mediated side effects.

Patients and Methods

Two of 9 pts with relapsed FL treated with PI3Kδ (pt1) and PI3Kα/δ (pt2) inhibitors developed severe adverse events (SAE). Both pts were heavily pretreated including autologous transplantation and discontinued therapy due to SAE. Pt1 showed grade 3 transaminase elevation, esophagitis and diarrhea requiring hospitalization after 3 cycles of therapy. Diarrhea worsened with fever and weight loss, in spite of transient discontinuation and dose reduction of PI3k inhibitor. Colonoscopic biopsy showed GVHD-like colitis. He died 3 months later. Pt2 has developed, after the first cycle and over a period of one year, febrile neutropenia, erythroderma, ulcerative keratitis requiring corneal transplant, pure red cell aplasia, endocrine abnormalities, grade 3 diarrhea with weight loss, and inflammatory bowel disease-like colitis.

Detailed T-cell subpopulations immunophenotyping and T-cell receptor (TCR) spectratyping were performed in samples obtained at 6 months and 1 year after the start of treatment.

Results

Compared to healthy controls (HC)  both pts showed marked abnormalities in T-cell subsets including a very low percentage of CD4+CD45RA+CCR7+CD31+ recent T-emigrants (RTE) and of CD4+CD45RA+CCR7+ naïve T cells in both CD4+ and CD8+ populations; CD4+CD45RA-CCR7+ central memory were significantly decreased, while CD4+CD45RA-CCR7- effector memory T cells were increased. Natural CD4+CD25+CD127low/- regulatory T cell (Treg) were low in both pts and the defect equally involved naïve, central and effector memory Treg. On the contrary, inducible Treg (Tr1) did not differ between FL pts and HC.

The predominance of effector T cells strongly biased the TCR repertoire. Cells expressing all TCR beta variable (BV) chains were clonally or oligoclonally expanded at the spectratyping analysis because their profiles deviated from the Gaussian patterns found in polyclonal repertoires of HC.

Discussion

The clinical picture of the two FL pts was reminiscent of congenital immunodeficiencies with defects of Treg activity (e.g. IPEX caused by FoxP3 gene mutation). Similar symptoms and T-cell abnormalities are also present in pts with inadequate thymic function and immunologic reconstitution due to severe chronic GVHD. The associated T-cell immunological derangement was characterized by: 1) a marked reduction of the thymic output; 2) a clear defect in natural Treg; 3) an increase of peripheral oligoclonal effector memory T cells. Preclinical data on the role of PI3kδ support its possible pathogenetic involvement: PI3Kδ is known to play critical roles during thymopoiesis and its deletion/inactivation results in a block at the CD4 CD8 double negative stage of T-cell development. In mice with a mutation of PI3Kδ subunit, Treg were increased in the thymus but decreased in all peripheral immune organs, suggesting an impaired emigration of these cells from the thymus. Moreover, mice expressing an inactive form of PI3Kδ develop inflammatory bowel disease.

These preliminary data suggest that small molecule-mediated inhibition of PI3Kδ may cause severe alterations within the T-cell compartment in selected pts, which may derive from a defect in the thymic output, including that of Treg. The generation of mature, oligoclonal T cells can be either the result of an homeostatic T-cell proliferation or of a strong (auto)antigenic stimulation. To better elucidate such mechanisms, further studies are in progress on a larger number of pts showing different levels of PI3k inhibitor toxicity. Nevertheless, we suggest that a close follow-up of lymphocyte subpopulation changes should be worthwhile since it may anticipate the onset of these severe clinical manifestations.