Originally published as JCO Early Release 10.1200/JCO.2005.09.923 on December 21 2004
CTLA-4 Blockade: Unveiling Immune Regulation
Glenn Dranoff
Department of Medical Oncology, Dana-Farber Cancer Institute; Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
To maintain tissue homeostasis under the duress of infection or injury, the immune system is endowed with a diverse repertoire of soluble and cellular effectors. The innate response, composed of granulocytes, macrophages, dendritic cells, natural killer cells, and complement, is rapidly triggered into action, detecting tissue disturbance through a set of germline-encoded pattern recognition receptors. The adaptive reaction, consisting of antibody-producing B cells and T lymphocytes, is slower to develop, but manifests exquisite specificity and memory. These attributes reflect the requirement for expansion of rare clones harboring somatically rearranged immunoglobulin molecules or T-cell receptors specific for foreign proteins or processed peptides presented by major histocompatibility complex (MHC) molecules. These innate and adaptive responses are carefully orchestrated through soluble and membrane-bound regulators, resulting in the deployment of the most suitable effectors for containing the disorder, while minimizing tissue damage.
Cancer cells similarly provoke immune recognition. In one pathway, innate effectors detect tumor cells directly.1 Natural killer cells and phagocytes express NKG2D molecules that function as receptors for stress-related genes such as MICA and MICB, which are induced as a consequence of cellular transformation. Natural killer cells further scan for the loss of MHC class I molecules on the surface of tumor cells. Dendritic cells use a variety of scavenger receptors to result in the phagocytosis of dying tumor cells.
The adaptive response exploits an indirect pathway, termed cross-priming, to recognize cancer cells.2 In this mechanism, dendritic cells capture tumor cell debris, migrate to regional lymph nodes, and stimulate CD4+ and CD8+ T cells with tumor specificity. Primed T cells thereby acquire the capacity to detect tumor cells directly in a MHC-restricted fashion. CD4+ T cells also contribute to B-cell antibody production.
Antitumor innate and adaptive responses are frequently detected in cancer-bearing hosts, but their biologic importance remains incompletely understood. In some cases, endogenous reactions may function to attenuate disease progression. In multiple cancer types, clinicopathologic studies of early-stage lesions demonstrate that dense intratumoral lymphocyte infiltrates are strongly correlated with reduced frequencies of metastasis and improved patient survival.3 Moreover, in advanced ovarian carcinoma, lymphocyte infiltrates also predict for complete responses and prolonged survival following cytotoxic therapy.4 Consistent with this protective role, several strains of immune-deficient mice display enhanced susceptibility to spontaneous and carcinogen-induced tumors.5 Nonetheless, other compelling data indicate that tumor cells sometimes exploit host responses to promote disease progression.6 Unresolved inflammation may facilitate tumor development by modulating tumor cell growth, apoptosis, invasion, and metastasis. Together, these divergent outcomes underscore a dual role for immunity in carcinogenesis.7
Source:http://jco.ascopubs.org/cgi/content/full/23/4/662
CTLA-4 Blockade: Unveiling Immune Regulation
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Jimmy B
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