Genetic variation in the in vitro veto activity of bone-marrow cells

Treatment of an autoimmune disease with "classical" T cell veto: a proposal

Immune responses protect against infectious diseases and cancers. In normal circumstances, the immune system is tolerant to self. However, under certain conditions this tolerance is broken. The immune system attacks otherwise normal tissue. An autoimmune disease ensues. Strategies are now being sought that remove the pathogenic T cells without affecting other immune functions. "Classical" veto has been described as an immune suppressive mechanism able to remove T cells in a highly specific and effective manner. The present article briefly reviews the current knowledge on the development of autoreactive T cells and their regulation in the periphery. It describes "classical" veto, its mechanisms, and its novel applications. Finally, it argues that "classical" veto can be adapted to treat an autoimmune disease, such as type I diabetes mellitus.

Hybrid antibody mediated veto of cytotoxic T lymphocyte responses

Strategies are being sought that allow the induction of specific tolerance to allogeneic transplants without affecting other immune functions. The so-called veto effect has been described as one such technology where CD8+ cells suppress responses of class I MHC-restricted T-lymphocyte precursors to antigens expressed by those CD8+ veto cells. Yet, veto inhibition will not be able to provide complete tolerance to allogeneic grafts since it only operates on cell populations that express CD8. Other types of cells prevalent in most organs express different tissue-specific antigens that are recognized by alloreactive T-cells. Therefore, complete tolerance to an allogeneic transplant can only be achieved if all cellular components within the graft acquire the immune-inhibitory function. Here, we studied whether the veto effect could be exploited for this purpose nevertheless. We produced a hybrid antibody (HAb) combining a mAb specific for a class I MHC molecule with a soluble CD8 molecule. We found that this HAb specifically and effectively transferred veto inhibition to different stimulator cell populations. Thus, we have developed a strategy that promises to selectively and completely tolerize graft-specific CTLs without affecting normal immune responses.

Veto function in vitro and in vivo

A CTLp recognizing another cell, called veto cell, is suppressed by that veto cell. The veto cell can itself be a CTL. For the veto function, the TCR of the veto cell is not required, hence the veto function is a backward action of CTL. Since, from the point of view of the veto cell, only self-reactive CTLp are suppressed, the veto function could be a mechanism for maintaining self tolerance of CTL. The characteristics of veto function in vitro and in vivo are discussed, as well as the potential physiological relevance.