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Beta-glucan enhanced killing of renal cell carcinoma micrometastases by monoclonal antibody G250 directed complement
Cornelis F M Sier1, Kyra A Gelderman, Frans A Prins
1Department of Pathology, Leiden University Medical Center, Leiden, The Netherlands. C.F.M.Sier@lumc.nl
Abstract:
Metastases from renal cell carcinomas (RCC) are resistant to radiation and chemotherapy but are relatively immunogenic. We have investigated the possibility to eliminate human RCC micrometastases using MAb G250. G250 penetrates human micrometastases completely in a spheroid model and induces complement deposition rapidly on the outmost cell layers. However, complement dependent cytotoxicity (CDC) was barely detected using either (51)chromium release assays or confocal microscopy, due to relatively low expression of the G250 antigen and the effect of membrane bound complement regulatory proteins. Addition of blocking anti-CD59 MAbs enhanced formation of C5b-9 and consequently complement mediated lysis (13%). Complement assisted cellular cytotoxicity (CACC) was not detectable, although the iC3b ligand and CR3 receptor were present on respectively target and effector cells. Addition of soluble beta-glucan induced the killing of MAb and iC3b opsonized spheroids by effector cells (6-21%). Despite a lower affinity for G250 antigen, a bispecific anti-G250*anti-CD55 MAb enhanced cell killing in spheroids comparable to the parental G250 MAb. Our results suggest that complement-activating G250 in combination with anti-mCRP MAbs is able to kill human RCC cells in micrometastasis in vitro. For CACC the presence of CR3-priming beta-glucan seems to be obligatory. In vivo, bi-MAb may be more effective as therapeutic agent due to its increased C5a generating properties.
Insights
Monoclonal antibody G250 shows potential for eliminating renal cell carcinoma (RCC) micrometastases. Combining G250 with complement regulatory protein blockers enhances cell killing, suggesting a promising therapeutic strategy for RCC.
Area of Science:
- Oncology
- Immunology
- Biochemistry
Background:
- Metastatic renal cell carcinoma (RCC) exhibits resistance to conventional therapies.
- RCC micrometastases are immunogenic, presenting a potential target for immunotherapy.
Purpose of the Study:
- To investigate the efficacy of monoclonal antibody (MAb) G250 in eliminating human RCC micrometastases.
- To explore strategies for enhancing MAb G250-mediated tumor cell killing.
Main Methods:
- Utilized a spheroid model to simulate human RCC micrometastases.
- Assessed complement-dependent cytotoxicity (CDC) using chromium release assays and confocal microscopy.
- Investigated the role of complement regulatory proteins (e.g., CD59, CD55) and complement-assisted cellular cytotoxicity (CACC).
- Evaluated the impact of beta-glucan and bispecific antibodies on MAb G250 efficacy.
Main Results:
- MAb G250 penetrated RCC spheroids and induced complement deposition.
- Limited CDC was observed due to low antigen expression and membrane-bound complement regulatory proteins.
- Blocking anti-CD59 MAbs enhanced complement-mediated lysis.
- Addition of beta-glucan facilitated MAb and iC3b opsonized spheroid killing.
- A bispecific anti-G250*anti-CD55 MAb showed comparable cell killing to G250.
Conclusions:
- Complement-activating G250, combined with anti-membrane complement regulatory protein (mCRP) MAbs, can kill human RCC cells in micrometastases in vitro.
- Beta-glucan appears essential for CR3-mediated CACC.
- Bispecific antibodies targeting G250 may offer enhanced therapeutic potential in vivo due to increased C5a generation.
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