Novel immunotherapy approaches to follicular lymphoma

Translational insights into the genetics and immunobiology of relapsed/refractory follicular lymphoma

Although follicular lymphoma (FL) is traditionally classified as an indolent subtype of B cell non-Hodgkin lymphoma, clinical trajectories are often diverse based on unique disease biology, and many patients will eventually experience relapse of their disease. Furthermore, progression of disease within 24 months is associated with increased mortality rates for FL. In the last five years, we have witnessed an upsurge in the commercial availability of targeted therapies for relapsed/refractory (R/R) FL, including chimeric antigen receptor-T (CAR-T) products, bispecific T cell engagers (BiTEs), epigenetic modifier therapies, and next-generation Bruton tyrosine kinase (BTK) inhibitors. Furthermore, clinical trial options have increased tremendously and now include combinatorial strategies that exert synergy against malignant germinal center B cells. Here, we provide a 2024 update of novel therapeutic agents whose development has been informed by recent advances in the genetics and immunobiology of R/R FL. Specifically, we emphasize high-value targeted therapeutics, including anti-CD3 x anti-CD20 BiTEs and adoptive T cell therapies. We discuss prospects on selection and sequencing of BiTEs and CAR-T therapies for patients with R/R FL. We underscore the principles of FL pathobiology that are paving way for future drug discovery and shed insight into therapeutic targeting within nodal basins based on our increasing understanding of the FL microenvironment. Finally, we summarize how a greater knowledge of FL immunobiology can inform risk stratification and therapy selection on a personalized basis for R/R FL in 2025.

The clinical and molecular taxonomy of t(14;18)-negative follicular lymphomas

Follicular lymphoma (FL) is a neoplasm derived from germinal center B cells, composed of centrocytes and centroblasts, with at least a focal follicular growth pattern. The t(14;18) translocation together with epigenetic deregulation through recurrent genetic alterations are now recognized as the hallmark of FL. Nevertheless, FL is a heterogeneous disease, clinically, morphologically, and biologically. The existence of FL lacking the t(14;18) chromosomal alteration highlights the complex pathogenesis of FL, and indicates that there are alternative pathogenetic mechanisms that can induce a neoplasm with follicular center B-cell phenotype. Based on their clinical presentation, t(14;18)-negative FLs can be divided into 3 broad groups: nodal presentation, extranodal presentation, and those affecting predominantly children and young adults. Recent studies have shed some light into the genetic alterations of t(14;18)-negative FL. Within the group of t(14;18)-negative FL with nodal presentation, cases with STAT6 mutations are increasingly recognized as a distinctive molecular subgroup, often cooccurring with CREBBP and/or TNFRSF14 mutations. FL with BCL6 rearrangement shows clinicopathological similarities to its t(14;18)-positive counterpart. In contrast, t(14;18)-negative FL in extranodal sites is characterized mainly by TNFRSF14 mutations in the absence of chromatin modifying gene mutations. FL in children have a unique molecular landscape when compared with those in adults. Pediatric-type FL (PTFL) is characterized by MAP2K1, TNFRSF14, and/or IRF8 mutations, whereas large B-cell lymphoma with IRF4 rearrangement is now recognized as a distinct entity, different from PTFL. Ultimately, a better understanding of FL biology and heterogeneity should help to understand the clinical differences and help guide patient management and treatment decisions.

Follicular Lymphoma Microenvironment Characteristics Associated with Tumor Cell Mutations and MHC Class II Expression

Follicular lymphoma (FL) is a B-cell malignancy with a complex tumor microenvironment that is rich in nonmalignant immune cells. We applied single-cell RNA sequencing to characterize the diverse tumor and immune cell populations of FL and identified major phenotypic subsets of FL T cells, including a cytotoxic CD4 T-cell population. We characterized four major FL subtypes with differential representation or relative depletion of distinct T-cell subsets. By integrating exome sequencing, we observed that somatic mutations are associated with, but not definitive for, reduced MHC expression on FL cells. In turn, expression of MHCII genes by FL cells was associated with significant differences in the proportions and targetable immunophenotypic characteristics of T cells. This provides a classification framework of the FL microenvironment in association with FL genotypes and MHC expression, and informs different potential immunotherapeutic strategies based upon tumor cell MHCII expression.

SIGNIFICANCE

We have characterized the FL-infiltrating T cells, identified cytotoxic CD4 T cells as an important component that is associated with tumor cell-intrinsic characteristics, and identified sets of targetable immune checkpoints on T cells that differed from FLs with normal versus low MHC expression. See related commentary by Melnick, p. 374. This article is highlighted in the In This Issue feature, p. 369.

Phase 1/2 study of intratumoral G100 (TLR4 agonist) with or without pembrolizumab in follicular lymphoma

Intratumoral injection of G100, a toll-like receptor 4 (TLR4) agonist, was shown pre-clinically to stimulate anti-tumor immune responses and tumor regression. This open-label, multicenter, phase 1/2 trial evaluated the safety, tolerability, and preliminary efficacy of intratumoral G100 injections following localized low-dose radiation in patients with follicular lymphoma (ClinicalTrials.gov #NCT02501473). The study was comprised of a G100 dose escalation (5 or 10 µg/dose, or 20 µg/dose for large tumors); a randomized component comparing G100 to G100 plus pembrolizumab; and G100 20 µg/dose expansion. Adverse events grade ≥3 were uncommon in patients treated with G100, and no unexpected toxicities were observed when combined with pembrolizumab. G100 20 µg (n = 18) resulted in an overall response rate of 33.3% and abscopal tumor regression in 72.2% of patients. This early-phase study provides a foundation for combining an intratumoral TLR4 agonist with agents to produce immune-mediated responses in follicular lymphoma with limited added toxicity.

Novel aspects on gonadotoxicity and fertility preservation in lymphoproliferative neoplasms

The topic of fertility preservation in patients with a lymphoproliferative disease offers new aspects of debate, due to the introduction of novel chemotherapeutic regimens and small molecules in the clinical landscape. Cancer related infertility is mostly dependent on gonadotoxic treatments and fertile female patients are today addressed to the oocyte cryopreservation or to ovarian cortex fragment cryopreservation. These methods present advantages and disadvantages, which will be discussed in the present review, together with the options for male patients. The recent discovery of functional ovarian stem cells (OCSs) in woman ovarian cortex, opens new avenues offering a innovative procedure for fertility preservation through as model of regenerative medicine. Here, we review the gonadotoxic potential of "classical" chemotherapeutic treatments as well as of "novel" targeted therapies actually employed for lymphoproliferative neoplasms in young patients and revisit both the today available and future chances to preserve and restore fertility after the cancer healing.

One Size Does Not Fit All: Who Benefits From Maintenance After Frontline Therapy for Follicular Lymphoma?

Follicular lymphoma (FL) is the second most common non-Hodgkin lymphoma and the most common indolent B-cell malignancy. The disease often presents in advanced stage and can often be observed before initiation of therapy. Although the incidence is only approximately 15,000 new cases per year, the prevalence is substantially higher owing to the favorable overall survival (OS) of most patients. The most impactful advance responsible for the improvement of OS in FL was the introduction of the anti-CD20 monoclonal antibody (mAb) rituximab over 20 years ago. Phase III trials demonstrate that rituximab improves the OS in FL when combined with chemotherapy. However, unlike aggressive B-cell lymphomas, advanced stage FL is generally incurable and often displays a pattern of progressively shorter remissions with subsequent lines of therapy. Hence, maintenance strategies have been developed to prolong remissions achieved with frontline therapy. The value of maintenance after frontline therapy has been most extensively studied with extended treatment of anti-CD20 mAb, but recent approaches include chemotherapy-free combinations and targeted therapies given for extended durations. Here, we review relevant data that provide rationale in support of maintenance therapy in FL as well as the risks and limitations of a "one-size-fits-all" approach. Importantly, we note the biologic and clinical heterogeneity across patients with FL that must be considered when making clinical decisions. Finally, we highlight ongoing research that explores response-adapted approaches based on the depth of response as defined by PET scans and assays for minimal residual disease (MRD) that aim to better personalize individual management strategies.