In the 1990’s while at the National Institutes of Health I wanted to understand mechanisms of HIV-1 entry and its transmission. In collaboration with Hana Goldingwe discovered the mechanism by which coreceptors mediate HIV-1 entry – by formation of a trimolecular complex with gp120 and CD4,and I suggested specific model of this complex. I also was performing experiments with live HIV-1 in Malcolm Martin’s laboratory and observed a regularity in the peaks of infection – every 10-fold dilution of the virus resulted in about 2 days delay in the peak of infection (ref. 1). I developed a mathematical model of the transmission of the virus in tissue cultures and found that the cell-to-cell transmission is much more effective than transmission by a cell-free virus. This finding had a major impact in the HIV-1 field providing a mechanism for fast transmission in vivo.

I was fascinated by the power of phage display and in collaboration with Dennis Burton identified and characterized a potent broadly neutralizing Fab, X5 (ref. 2) which provided important information for sterically restricted epitopes. My group developed large human antibody domain libraries and identified for the first time a very potent broadly neutralizing domain, m36 (ref. 3). Later using the power of phage display and structure- based design we succeeded to engineer very stable soluble one domain CD4, mD1.22, which in multivalent format was combined with m36 resulting in exceptionally potent molecule which neutralized all tested isolates (ref. 4). These molecules were used to generate effective CAR T cells which will be evaluated in clinical trial.

1. Dimitrov DS, Willey RL, Sato H, Chang L-J, Blumenthal R, Martin MA. Quantitation of human immunodeficiency virus type 1 infection kinetics. J. Virol. 67: 2182-2190, 1993. PMCID: PMC240333.

2. Moulard M, Phogat S, Shu Y, Xiao X, Binley JM, Zhang MY, Robinson J, Parren PWHI, Burton DR, Dimitrov DS. Novel broadly cross-reactive HIV-1 neutralizing human monoclonal Fab selected for binding to gp120-CD4-CCR5 complexes. PNAS. 2002 99: 6913-6918. PMCID: PMC124503.

3. Chen W, Zhu Z, Feng Y, Dimitrov DS. Human domain antibodies to conserved sterically restricted regions on gp120 as exceptionally potent cross-reactive HIV-1 neutralizers. PNAS. 2008 Nov 4; 105(44): 17121-17126. PMCID: PMC2579388.

4. Chen W, Feng Y, Prabakaran P, Ying T, Wang Y, Sun J, Macedo CD, Zhu Z, He Y, Polonis VR, Dimitrov DS. Exceptionally potent and broadly cross-reactive, bispecific multivalent HIV-1 inhibitors based on single human CD4 and antibody domains. J Virol. 2014 Jan; 88: 1125-39. PMCID: PMC3911630.

In the 2000’s I finally was able to fulfill a childhood dream – to develop therapeutics against viruses which could save human lives. My long-term collaborator, Chris Broder, has cloned and characterized the envelope glycoproteins of two newly identified emerging viruses which cause diseases of high (up to 90%) mortality, Hendra and Nipah viruses. We had the idea to use human monoclonal antibodies (mAbs) for therapy of exposed humans. We identified the first such mAbs in my group and one of them, m102.4 (ref. 1), was extensively evaluated in animal models of infection by Hendra and Nipah. The results were amazing – although infected monkey die within 10 days after challenge, m102.4 administered even 5 days post infection saved them although they were very sick. These results were followed by human clinical trial phase I with 40 volunteers which was completed successfully in Australia. Currently, m102.4 is approved for use in Australia on compassionate basis, the first mAb approved as a therapeutic against a viral disease. We also developed potent broadly neutralizing mAbs against other emerging viruses including the SARS-CoV (ref. 2), MERS-CoV (ref. 3) and SARS-CoV-2 (ref. 4) which all exhibited exceptionally potent neutralizing activity in animal models of viral infections, and the mAbs against MERS-CoV and SARS-CoV-2 are in production for evaluation in human clinical trials.

1. Zhu Z, Bossart KN, Bishop KA, Crameri G, Dimitrov AS, McEachern JA, Feng Y, Middleton D, Wang L-F, Broder CC, Dimitrov DS. Exceptionally potent cross-reactive neutralization of Nipah and Hendra viruses by a human monoclonal antibody. J. Infect. Dis. 197(6): 846-853, 2008. PMID: 18271743.

2. Zhu Z, Chakraborti S, He Y, Roberts A, Sheahan T, Xiao X, Hensley LE, Prabakaran P, Rockx B, Sidorov IA, Corti D, Vogel L, Feng Y, Kim J-O, Wang L-F, Baric R, Lanzavecchia A, Curtis KM, Nabel GJ, Subbarao K, Jiang S, Dimitrov DS. Potent cross-reactive neutralization of SARS coronavirus isolates by human monoclonal antibodies. PNAS 104(29): 12123- 12128, 2007. PMCID: PMC1924550.

3. Ying T, Du L, Ju TW, Prabakaran P, Lau CC, Lu L, Liu Q, Wang L, Feng Y, Wang Y, Zheng BJ, Yuen KY, Jiang S, Dimitrov DS. Exceptionally potent neutralization of MERS-CoV by human monoclonal antibodies. J. Virol. 2014 Jul; 88:7796-805. PMCID: PMC4097770.

4. Li W, Schäfer A, Kulkarni SS, Liu X, Martinez DR, Chen C, Sun Z, Leist SR, Drelich A, Zhang L, Ura ML, Berezuk A, Chittori S, Leopold K, Mannar D, Srivastava SS, Zhu X, Peterson EC, Tseng CT, Mellors JW, Falzarano D, Subramaniam S, Baric RS, Dimitrov DS. High potency of a bivalent human VH domain in SARS-CoV-2 animal models. Cell, 183, 429–441, 2020.

In the 2000’s my laboratory was one of the few in the world if not the only one which has identified broadly neutralizing mAbs (bnAbs) against emerging viruses and HIV-1. I was puzzled by the dramatic contrast in the level of somatic hypermutation between those mAbs – very low vs very high. I thought that HIV-1 has evolved to protect its highly conserved epitopes by not exposing them to the germline precursors of bnAbs. Thus, I suggested to test the bnAb germline precursors whether they bind to the HIV-1 envelope glycoprotein (Env) (ref. 1-4). Theresult was exciting – they did not as I hypothesized. Therefore, a successful vaccine should target the germline bnAb predecessors toinitiate the immune response (ref. 3). Many articles appeared one-two years after my original suggestion and my colleagues were successful to construct such potential vaccine immunogens. However, the second challenge, the complexity of the antibody maturation pathways remains unsolved although I hope that we could be lucky and finally discover a promising vaccine immunogen.

1. Xiao X, Chen W, Feng Y, Zhu Z, Prabakaran P, Wang Y, Zhang M-Y, Longo NS, Dimitrov DS. Germline-like predecessors of broadly neutralizing antibodies lack measurable binding to HIV-1 envelope glycoproteins: implications for evasion of immune responses and design of vaccine immunogens. BBRC 2009 Dec 18;390(3):404-9. Epub 2009 Sep 11. PMCID: PMC2787893.

2. Xiao X, Chen W, Feng Y, Dimitrov DS. Maturation pathways of cross-reactive HIV-1 neutralizing antibodies. Viruses, 1: 802-817, 2009. PMCID: PMC3185542.

3. Dimitrov DS. Antibody therapeutics, vaccines and antibodyomes. mAbs 2: 347-356, 2010. PMCID: PMC2881260.

4. Dimitrov DS. Method of making vaccines – patent application filed by NCI, September 2008.

In the 2000’s we began also to develop human mAbs against cancer.One of the first target was CD22 which is expressed on B cells and could be used for elimination of cancer cells. One of the mAbs identified in my laboratory, m971 (ref. 1), was used to make chimeric antigen receptors (CARs) which were expressed on the surface ofT cells (ref. 2). The m971-based CAR-T cell therapy was highly successful in animal models of cancer and in humans (ref. 3). The patentcovering m971 mAb was licensed by Juno. Currently, m971 is used in many clinical trials especially when there is escape from the CD19targeting CARs. We developed a number of other mAbs some of which have been tested in animal models and one of them, m912 (ref. 4), against mesothelin, was licensed to Atara biotherapeutics and is in human trials at Sloan Kettering.

1. Xiao X, Ho M, Zhu Z, Pastan I, Dimitrov DS. Identification and characterization of fully human anti-CD22 monoclonal antibodies. mAbs 1: 297-303, 2009. PMCID: PMC2726586. (US patent 8,591,889 issued November 26, 2013)

2. Haso W, Lee DW, Shah NN, Stetler-Stevenson M, Yuan CM, Pastan IH, Dimitrov DS, Morgan RA, FitzGerald DJ, Barrett DM, Wayne AS, Mackall CL, Orentas RJ. Anti- CD22-Chimeric Antigen Receptors Targeting B Cell Precursor Acute Lymphoblastic Leukemia. Blood 121(7): 1165-1174, 2013. PMCID: PMC3575759.

3. Fry TJ, Shah NN, Orentas RJ, Stetler-Stevenson M, Yuan CM, Ramakrishna S, Wolters P, Martin S, Delbrook C, Yates B, Shalabi H, Fountaine TJ, Shern JF, Majzner RG, Stroncek DF, Sabatino M, Feng Y, Dimitrov DS, Zhang L, Nguyen S, Qin H, Dropulic B, Lee DW, Mackall CL. CD22-targeted CAR T cells induce remission in B-ALL that is naive or resistant to CD19-targeted CAR immunotherapy. Nat Med. 2018 Jan; 24(1):20-28. PMCID: PMC5774642.

4. Feng Y, Xiao X, Zhu Z, Streaker E, Ho M, Pastan I, Dimitrov DS. A novel human monoclonal antibody that binds with high affinity to mesothelin-expressing cells and kills them by antibody-dependent cell-mediated cytotoxicity. Mol. Cancer Ther. 2009 8(5): 1113-8. PMCID: PMC2891957.