Jian Li Campian, MD, PhD
Assistant Professor of Medicine
Siteman Cancer Center
Washington University School of Medicine
St. Louis, MO
The concept that the immune system plays a pivotal role in the prevention and control of cancer is not new to the literature. In recent years, this has led to an explosion in immunotherapy research and the FDA approval of sipuleucel-T, nivolumab, pembrolizumab, and ipilimumab. Now, brain cancer researchers are exploring whether replenishing the immune system of patients with high-grade glioma who have undergone cytotoxic treatment can improve outcomes.
To do so, researchers at Washington University in St. Louis and elsewhere are focusing on lymphocytes, the essential effector cells in the immune response to cancer.1
The presence of adequate circulating lymphocytes appears correlated with the pharmacological efficacy of the immune checkpoint–blocking agent ipilimumab and the anticancer vaccine sipuleucel-T.2-4
Furthermore, the clinical consequences of lymphopenia have been well described. Pretreatment lymphopenia has been found to be a poor prognostic indicator in many cancers.5,6
The extent of lymphocytic infiltration of solid tumors on pathology has also been correlated with overall survival.7-10
More recently, lymphopenia following initiation of treatment with chemoradiation has been explored in various cancers, with findings showing inferior overall survival. Most notably, a prospective study consisting of 96 patients with high-grade glioma examined the association between CD4 cell counts and clinical outcomes. These patients received three highly lymphotoxic therapies: radiation (RT), glucocorticoids, and temozolomide (TMZ). Total lymphocyte counts (TLCs) and CD4 cell counts were normal prior to initiation of antineoplastic therapy.
However, 2 months following RT and TMZ, 40% of these patients suffered from severe grade 3-4 lymphopenia with a TLC <500 cells/mm3 and CD4 count <200 cells/mm3 with persistence of severe lymphopenia for more than a year. Multivariate analysis revealed these significant reductions in CD4 counts at 2 months were independently associated with inferior overall survival due primarily to tumor progression.11
The association between treatment-related lymphopenia and worse clinical outcomes has also been observed in non–small cell lung cancer, head and neck cancer, and pancreatic cancer.12-17
Recent studies suggest that radiation may play a major role in lymphopenia. Yovino et al used a mathematical model to estimate the radiation exposure of circulating lymphocytes during RT to the brain. They found that more than 95% of circulating cells received a lymphocyte toxic dose after the standard 30 fractions of radiation treatment.18
Since this lymphopenia is iatrogenic and associated with early tumor progression, additional studies are required to determine if the immune system can be restored after this treatment-induced damage. Correction of this treatment-related lymphopenia through an immunotherapeutic approach would represent a potential paradigm shift in the treatment of patients with highgrade glioma. However, the best way for reconstituting an immune response has not been established. Several approaches could be considered.
A study that was recently published explored the feasibility of harvesting circulating lymphocytes from patients prior to beginning RT/TMZ and then reinfusing the cryopreserved lymphocytes once radiation was complete. We enrolled 10 patients, with 8 of them completing both lymphocyte harvest and reinfusion.
Lymphocyte harvest and reinfusion were shown to be feasible in patients with high-grade glioma on dexamethasone, and no toxicities were noted. An increase in TLC >300 cells/mm3 was seen in 88% of the recipient patients during the 14-week observation period post reinfusion. However, CD4 cell counts were not improved by lymphocyte reinfusion.16
Interleukin-7 (IL-7) is the primary homeostatic cytokine of T cells in the peripheral blood. IL-7 plasma levels are inversely correlated with peripheral CD4 T-cell counts, similar to erythropoietin blood levels and their inverse correlation with red blood cell counts. Although IL-7 is limiting in normal conditions, it accumulates during lymphopenic conditions.19