Immune-competent cells of regional lymph nodes in colorectal cancer patients: II. Immunohistochemical analysis of Leu-7+ cells

Innate tumor killers in colorectal cancer

Standard treatment of colorectal cancer (CRC) improves the prognosis of CRC patients, but it is still intractable to control the progression of metastatic CRC. Immune microenvironment and immunotherapies of CRC have received extensive attention in recent years, but present immunotherapies of CRC have mainly focused on T cells and therapeutic response is only observed in a small proportion of patients. Innate immune cells are the first-line of defense in the development of malignancies. Natural killer (NK) cells, NKT cells and γδT cells are three types of innate cells of lymphoid origin and show cytotoxicity against various tumor cells including CRC. Besides, in the development of CRC, they can also be inhibited or express regulatory type, promoting tumor progression. Researches about anti-tumorigenic and pro-tumorigenic mechanisms of these cells are ongoing and regulation of these cells is also being unearthed. Meanwhile, immunotherapies using these cells more or less have shown efficacy in animal models and some of them are under exploration in clinical trials. This review provides an overview of intrinsic properties of NK cell, NKT cell and γδT cell, and summarizes current related promising treatment strategies.

Functional Significance of CD57 Expression on Human NK Cells and Relevance to Disease

Historically, human NK cells have been identified as CD3(-)CD56(+)CD16(±) lymphocytes. More recently it has been established that CD57 expression defines functionally discrete sub-populations of NK cells. On T cells, CD57 expression has been regarded as a marker of terminal differentiation and (perhaps wrongly) of anergy and senescence. Similarly, CD57 expression seems to identify the final stages of peripheral NK cell maturation; its expression increases with age and is associated with chronic infections, particularly human cytomegalovirus infection. However, CD57(+) NK cells are highly cytotoxic and their presence seems to be beneficial in a number of non-communicable diseases. The purpose of this article is to review our current understanding of CD57 expression as a marker of NK cell function and disease prognosis, as well as to outline areas for further research.

Immunotherapy of colorectal cancer

Specific and nonspecific stimulation of the host immune system to reject cancer is an attractive concept that is just beginning to mature. Results with crude extracts and nonspecific immune stimulation have been variable. However, the recent observations of improved survival after administration of levamisole plus 5-fluorouracil in the adjuvant setting have made an impact on the treatment of colorectal cancer. Animal studies consistently show that immune therapies are most effective for disease that is not advanced. Thus, the small benefit seen with levamisole, a low toxicity immunomodulator, suggests that much more impressive results can be anticipated with more potent and specific agents. Postsurgical autologous tumor cell vaccine has been effective in some prospective randomized trials; in others, no benefit was found. The identification and purification of allogeneic tumor-associated antigens has lead to enhanced antigen-specific host cell-mediated immunity; this may result in more consistent antitumor effects. The current development of chemically defined immune adjuvants of low toxicity allows tumor-specific immune stimulation to be tested in high-risk apparently healthy patients after resection of colorectal cancer (Stages II and III). The influx of information regarding immune cell populations, cell-surface markers, and cytokines has fostered extensive exploration of lymphocyte stimulation, in vitro cell growth and expansion, and in vivo evaluation in patients with advanced cancer. Modest tumor response rates have been documented with adoptive transfer of lymphokine-activated killer cells and interleukin-2. Improved results are anticipated with the more potent tumor-infiltrating lymphocytes and specific in vitro sensitization of draining lymph node cells to autologous and allogeneic tumor antigens. Murine monoclonal antibodies specific for cell-surface markers, such as carcinoembryonic antigen, have been tested for their value in the diagnosis and therapy of colorectal cancer. A small response rate has been seen with single and multiple injections of C017-1A, a monoclonal antibody specific for colonic and pancreatic cancer. The development of antiidiotypic antibodies in these patients may have been important in those that responded to this type of therapy. However, laboratory evidence suggests that monoclonal antibody conjugated to a cytotoxic agent (i.e., radionuclide, drug, or toxin) should be much more effective. Radioimmunotherapy trials in the nude mouse model bearing human colon cancer xenografts showed good tumor incorporation of the radionuclide (yttrium 90 or iodine 131), inhibition of tumor growth, and long-term survival.(ABSTRACT TRUNCATED AT 400 WORDS)