{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/151592"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/151592","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Mechanistic Elucidation and Therapeutic Improvement of Anti-CTLA-4 Therapies","abstract":"Anti-CTLA-4 antibodies have successfully elicited durable tumor regression in the clinic; however, long-term benefit is limited to a subset of patients for select cancer indications. The incomplete understanding of their mechanism of action has hindered efforts at improvement, with conflicting hypotheses proposing either antagonism of the CTLA-4:B7 axis or Fc effector-mediated regulatory T cell (Treg) depletion governing efficacy. Here we report the engineering of a non-antagonistic CTLA-4 binding domain (b1s1e2) that depletes intratumoral Tregs as an Fc fusion. Comparison of b1s1e2-Fc to 9d9, an antagonistic anti-CTLA-4 antibody, allowed for determination of the separate contributions of CTLA-4 antagonism and Treg depletion to efficacy. Despite equivalent levels of intratumoral Treg depletion, 9d9 achieved more long-term cures than b1s1e2-Fc in MC38 tumors, demonstrating that CTLA-4 antagonism provided additional survival benefit. Consistent with prior reports that CTLA-4 antagonism enhances priming, treatment with 9d9, but not b1s1e2-Fc, increased the percentage of activated T cells in the tumor-draining lymph node (tdLN). Treg depletion with both constructs was restricted to the tumor due to insufficient surface CTLA-4 expression on Tregs in other compartments to elicit Fc effector-mediated Treg depletion. Through intratumoral administration of diphtheria toxin (DT) in Foxp3-DTR mice, we show that depletion of both intratumoral and intranodal Tregs provided even greater survival benefit than 9d9, consistent with Treg-mediated restraint of priming in the tdLN. Lastly, we engineered a CTLA-4-targeted enzyme fusion as a potentially translatable approach for combined intratumoral and intranodal Treg depletion. Preliminary data suggest that CTLA-4 targeting increases local Treg death as a result of proximal enzymatic activity, but further characterization remains to be done. Overall, our data demonstrate that anti-CTLA-4 therapies require both CTLA-4 antagonism and intratumoral Treg depletion for maximum efficacy - but that future therapies capable of depleting intranodal Tregs could show superior efficacy, even in the absence of CTLA-4 antagonism.","abstract_html":"Anti-CTLA-4 antibodies have successfully elicited durable tumor regression in the clinic; however, long-term benefit is limited to a subset of patients for select cancer indications. The incomplete understanding of their mechanism of action has hindered efforts at improvement, with conflicting hypotheses proposing either antagonism of the CTLA-4:B7 axis or Fc effector-mediated regulatory T cell (Treg) depletion governing efficacy. Here we report the engineering of a non-antagonistic CTLA-4 binding domain (b1s1e2) that depletes intratumoral Tregs as an Fc fusion. Comparison of b1s1e2-Fc to 9d9, an antagonistic anti-CTLA-4 antibody, allowed for determination of the separate contributions of CTLA-4 antagonism and Treg depletion to efficacy. Despite equivalent levels of intratumoral Treg depletion, 9d9 achieved more long-term cures than b1s1e2-Fc in MC38 tumors, demonstrating that CTLA-4 antagonism provided additional survival benefit. Consistent with prior reports that CTLA-4 antagonism enhances priming, treatment with 9d9, but not b1s1e2-Fc, increased the percentage of activated T cells in the tumor-draining lymph node (tdLN). Treg depletion with both constructs was restricted to the tumor due to insufficient surface CTLA-4 expression on Tregs in other compartments to elicit Fc effector-mediated Treg depletion. Through intratumoral administration of diphtheria toxin (DT) in Foxp3-DTR mice, we show that depletion of both intratumoral and intranodal Tregs provided even greater survival benefit than 9d9, consistent with Treg-mediated restraint of priming in the tdLN. Lastly, we engineered a CTLA-4-targeted enzyme fusion as a potentially translatable approach for combined intratumoral and intranodal Treg depletion. Preliminary data suggest that CTLA-4 targeting increases local Treg death as a result of proximal enzymatic activity, but further characterization remains to be done. Overall, our data demonstrate that anti-CTLA-4 therapies require both CTLA-4 antagonism and intratumoral Treg depletion for maximum efficacy - but that future therapies capable of depleting intranodal Tregs could show superior efficacy, even in the absence of CTLA-4 antagonism.","abstract_has_math":false,"creators":["Lax, Brianna Marie"],"institution":"Massachusetts Institute of Technology","degree_name":"Doctoral","degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Chemical Engineering","school":null,"contributors":[],"advisors":["Wittrup, K. Dane"],"committee_chairs":[],"committee_members":[],"year":2023,"date_issued":"2023-06","date_published":"2023-06","updated_at":"2026-07-22T22:22:19Z","subjects":[],"languages":[],"rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"rights_urls":["https://rightsstatements.org/page/InC-EDU/1.0/"],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1721.1/151592","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Wittrup, K. Dane"]},{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. 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The incomplete understanding of their mechanism of action has hindered efforts at improvement, with conflicting hypotheses proposing either antagonism of the CTLA-4:B7 axis or Fc effector-mediated regulatory T cell (Treg) depletion governing efficacy. Here we report the engineering of a non-antagonistic CTLA-4 binding domain (b1s1e2) that depletes intratumoral Tregs as an Fc fusion. Comparison of b1s1e2-Fc to 9d9, an antagonistic anti-CTLA-4 antibody, allowed for determination of the separate contributions of CTLA-4 antagonism and Treg depletion to efficacy. Despite equivalent levels of intratumoral Treg depletion, 9d9 achieved more long-term cures than b1s1e2-Fc in MC38 tumors, demonstrating that CTLA-4 antagonism provided additional survival benefit. Consistent with prior reports that CTLA-4 antagonism enhances priming, treatment with 9d9, but not b1s1e2-Fc, increased the percentage of activated T cells in the tumor-draining lymph node (tdLN). Treg depletion with both constructs was restricted to the tumor due to insufficient surface CTLA-4 expression on Tregs in other compartments to elicit Fc effector-mediated Treg depletion. Through intratumoral administration of diphtheria toxin (DT) in Foxp3-DTR mice, we show that depletion of both intratumoral and intranodal Tregs provided even greater survival benefit than 9d9, consistent with Treg-mediated restraint of priming in the tdLN. Lastly, we engineered a CTLA-4-targeted enzyme fusion as a potentially translatable approach for combined intratumoral and intranodal Treg depletion. Preliminary data suggest that CTLA-4 targeting increases local Treg death as a result of proximal enzymatic activity, but further characterization remains to be done. Overall, our data demonstrate that anti-CTLA-4 therapies require both CTLA-4 antagonism and intratumoral Treg depletion for maximum efficacy - but that future therapies capable of depleting intranodal Tregs could show superior efficacy, even in the absence of CTLA-4 antagonism."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:title","label":"Title","values":["Mechanistic Elucidation and Therapeutic Improvement of Anti-CTLA-4 Therapies"]}]}],"canonical_facts":{"dc:contributor.advisor":["Wittrup, K. Dane"],"dc:contributor.department":["Massachusetts Institute of Technology. Department of Chemical Engineering"],"dc:creator":["Lax, Brianna Marie"],"dc:date.accessioned":["2023-07-31T19:51:04Z"],"dc:date.available":["2023-07-31T19:51:04Z"],"dc:date.issued":["2023-06"],"dc:description.abstract":["Anti-CTLA-4 antibodies have successfully elicited durable tumor regression in the clinic; however, long-term benefit is limited to a subset of patients for select cancer indications. The incomplete understanding of their mechanism of action has hindered efforts at improvement, with conflicting hypotheses proposing either antagonism of the CTLA-4:B7 axis or Fc effector-mediated regulatory T cell (Treg) depletion governing efficacy. Here we report the engineering of a non-antagonistic CTLA-4 binding domain (b1s1e2) that depletes intratumoral Tregs as an Fc fusion. Comparison of b1s1e2-Fc to 9d9, an antagonistic anti-CTLA-4 antibody, allowed for determination of the separate contributions of CTLA-4 antagonism and Treg depletion to efficacy. Despite equivalent levels of intratumoral Treg depletion, 9d9 achieved more long-term cures than b1s1e2-Fc in MC38 tumors, demonstrating that CTLA-4 antagonism provided additional survival benefit. Consistent with prior reports that CTLA-4 antagonism enhances priming, treatment with 9d9, but not b1s1e2-Fc, increased the percentage of activated T cells in the tumor-draining lymph node (tdLN). Treg depletion with both constructs was restricted to the tumor due to insufficient surface CTLA-4 expression on Tregs in other compartments to elicit Fc effector-mediated Treg depletion. Through intratumoral administration of diphtheria toxin (DT) in Foxp3-DTR mice, we show that depletion of both intratumoral and intranodal Tregs provided even greater survival benefit than 9d9, consistent with Treg-mediated restraint of priming in the tdLN. Lastly, we engineered a CTLA-4-targeted enzyme fusion as a potentially translatable approach for combined intratumoral and intranodal Treg depletion. Preliminary data suggest that CTLA-4 targeting increases local Treg death as a result of proximal enzymatic activity, but further characterization remains to be done. Overall, our data demonstrate that anti-CTLA-4 therapies require both CTLA-4 antagonism and intratumoral Treg depletion for maximum efficacy - but that future therapies capable of depleting intranodal Tregs could show superior efficacy, even in the absence of CTLA-4 antagonism."],"dc:description.degree":["Ph.D."],"dc:identifier.uri":["https://hdl.handle.net/1721.1/151592"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"dc:rights.uri":["https://rightsstatements.org/page/InC-EDU/1.0/"],"dc:title":["Mechanistic Elucidation and Therapeutic Improvement of Anti-CTLA-4 Therapies"],"dc:type":["Thesis"],"thesis:degree_name":["Doctoral","Doctor of Philosophy"]},"updated_at":"2026-07-22T22:22:19Z"}