Background/Purpose:

Adoptive transfer of regulatory T cells (Tregs)  represents a promising strategy for treatment of auto- and alloimmunity. However, it is difficult to obtain therapeutically relevant numbers of antigen-specific Tregs. Bispecific antibodies (bsAb) are promising tools for a target-specific redirection of polyclonal Tregs. BsAb are composed of two different antigen binding moieties facilitating the cross-linkage of two different cell types.  E.g. T cells redirected by bsAb to tumor cells result in an eradication of tumor cell as shown in various in vitro, in vivo and first clinical trials. Recently, we reported that bsAb can also be used for redirection of Tregs leading to the search of potential target structures in inflamed tissues. Many pathological immune-mediated conditions, e.g. autoimmune diseases, graft rejection or GvHD are associated with massive cell death. Recently, we established a cell culture system allowing us to unequevocally show that the nuclear autoantigen La is released from dying cells and tightly binds to neighbouring living intact cells. Therefore, we wanted to learn if La can be used as inducible surface target for redirection of subpopulations of T cells including Teff and Tregs via bsAbs.

Methods:

In order to induce cell death, cultured human cells were irradiated with UV. After irradiation human cells were cocultured with untreated murine cells. Human La released and bound to the surface of co-cultured murine cells was stained with three different anti-human La specific mabs (SW5, 5B9, 7B6). These mabs recognize well defined epitopes either in the N- (SW5, 5B9) or C-terminus (7B6) of La. Alternatively, recombinant human La was added to cultured human cells. Cell surface bound La was used for redirection of sorted Tregs via two novel bispecific anti-CD3-anti-La abs. The effects of sorted redirected Tregs on activation, cytokine release, killing efficacy, and proliferation of immune effector T cells were estimated by FACS.

Results:

Two novel fully humanized bsAb targeting La and the CD3 complex of T cells were established and their capability to redirect Teff and Tregs to surface bound La was tested. Both CD4+ and CD8+ Teff redirected to surface bound La resulted in an efficient killing of target cells while highly enriched sorted Tregs were not able to mediate cytotoxicity. In contrast, the cross-linkage of Tregs with La-decorated target cells resulted in activation of both freshly isolated and expanded human Tregs. Moreover, such bsAb-activated Tregs displayed a potent suppressive capacity and negatively influenced proliferation, expansion and cytokine production of autologous CD4+ and CD8+ Teff cells.

Conclusion:

Our results indicate that La released and tightly bound to the surface of living cells are accessible for abs and can therefore be used as inducible surface target for redirecting of T cell (sub)populations via bsAb. While redirected effector T cells mediate cell death Tregs can attenuate Teff cell-mediated inflammatory immune responses and tissue destruction and may therefore be useful for a site-specific recruitment of Tregs into inflamed tissues for the treatment of GvHD, autoimmunity or transplant rejection.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/bispecific-antibodies-for-redirection-of-human-regulatory-t-cells-to-surface-inducible-autoantigen-lass-b/