The virologist Robin Weiss, who has died aged 86, was the outstanding scientist of the UK’s response to the Aids pandemic. In 1984 he led the team that identified the CD4 molecule as the cellular receptor for HIV, the causative virus of Aids. Subsequently he established productive growth of HIV in an immortalised cell line, and this allowed the development, with Richard Tedder, of the UK’s first antibody test for HIV, later commercialised by the Wellcome Foundation.

Critically, this test allowed HIV-infected people to be identified accurately and at scale. Robin was the first to demonstrate antibody neutralisation of HIV, a fundamental basis to vaccine development. These major scientific advances were all achieved while Robin was the youngest-ever director (1980-89) of the Institute of Cancer Research (ICR) in London.

Robin was the son of Hans Weiss, a businessman, and Stefanie (nee Löwinsohn), secular German-Jewish refugees who had arrived in the UK in 1935; in 1940, the year of Robin’s birth, his father was interned in Scotland as an enemy alien. Born and brought up in London, Robin went as a boarder to Abbotsholme school in Staffordshire, then he took a first-class degree in zoology at University College London. Uncertain of his future career, he consulted his head of department, the Nobel laureate Peter Medawar, who suggested he should consider research.

Robin remained at UCL for his PhD, supervised by Michael Abercrombie, a cell biologist who had succeeded Medawar. Robin’s thesis, on the way that Rous sarcoma retrovirus infection in chickens transforms normal cells so that they proliferate in an uncontrolled way (causing cancer), was his first exposure to the retroviruses that were to define his career.

Retroviruses are an ancient family of RNA viruses affecting vertebrates, with the unique ability to produce a DNA copy from their RNA genome, which can then incorporate permanently into the host genome. They are widespread in animals, birds and, now, humans.

It was in Abercrombie’s UCL lab, as a lecturer in embryology (1963-70), that Robin published his landmark paper on endogenous retroviruses. Observing that some embryonic chick fibroblasts (connective tissue cells) allowed the release of infectious RSV, which always requires a “helper” virus to replicate, he hypothesised that normal embryo cells must already contain an integrated “endogenous” retrovirus.

His first paper was rejected, with one reviewer stating that Robin’s interpretation was impossible. A chance visit to UCL by Howard Temin, a Nobel prize-winning US retrovirologist, encouraged Robin to resubmit. We now recognise that endogenous retroviruses are not only widespread in nature – they constitute nearly 10% of the human genome.

In 1970, Robin won a fellowship to join Peter Vogt’s lab at the University of Southern California to study endogenous retroviruses (ERVs) in chickens. His curiosity over their origin led him to Malaysia, where he demonstrated that chicken ERVs were present in the ancestor species, the Malaysian red jungle fowl, preceding domestication.

In 1972, Robin was recruited by Sir Michael Stoker to the Imperial Cancer Research Fund laboratories at Lincoln’s Inn Fields in London, to study viral oncogenes, the cancer-causing genes found in retroviruses, which had been shown to be linked to human cancers. There he began his two-volume book RNA Tumor Viruses (published in 1982 and 1985) with Harald Varmus, Natalie Teich and John Coffin; this became the retroviral bible.

In 1979, Robin was approached by Sir Richard Doll, chair of the ICR, to apply for the role of director; Medawar, a member of the ICR board, encouraged him to take the post. Robin immediately set about transforming the institute, recruiting two young cell and molecular biologists, Chris Marshall and Alan Hall; together, they reported a novel oncogene known as N-RAS. Under Robin’s attentive support, these scientists had an immensely productive decade investigating the molecular mechanism of the N-RAS oncogene on cell proliferation and its cellular signalling pathway via the RAS-MAP kinase cascade, mutations of which underlie many human cancers. This work laid the scientific basis for the later development of successful anti-cancer drugs. Robin himself studied the newly discovered human retrovirus, the human T-cell leukaemia virus (HTLV).

In 1984 a new human retrovirus, HIV-1, was confirmed as the cause of Aids. Recognising the Aids pandemic as a public health emergency, Robin immediately pivoted his lab to work on this new virus. Although preferring to run a small laboratory, Robin willingly accepted the urgent need to train scientists and doctors to work on HIV; his laboratory rapidly became the UK centre for HIV retrovirology.

Robin was remarkably generous with his time and expertise; he was a sought-after expert adviser on HIV to the Medical Research Council, the Department of Health, the pharmaceutical industry, and to international agencies, symposia and conferences.

He was a willing scientific collaborator and a prolific commentator; his many articles for the journal Nature on HIV were elegantly written, incisive and influential. His lab became a magnet for ambitious students, post-docs and sabbatical researchers. It is a measure of his dedicated mentorship that all the 12 scientists who moved through his lab in the later 1980s subsequently enjoyed professorial university appointments.

Robin returned to UCL as professor of viral oncology in 1999. He seized on new-found freedom from administration to broaden his research interests. With Jonathan Stoye he returned to endogenous retroviruses, investigating PERV viruses in pigs, investigating their potential for reactivation following porcine kidney xeno-transplantation into humans. He made monoclonal “nanobodies” from llamas, a species chosen as they naturally made single chain antibodies and hence physically small molecules, potentially able to insert into narrow antigenic clefts.

He also solved the longstanding riddle of canine venereal sarcoma, a sexually transmissible cancer of dogs worldwide where the transmissible agent is uniquely a cancer cell itself. Robin showed that this tumour derived from a single dog, about 1,000 years ago. As with many of Robin’s projects, this eclectic subject posed a deeper scientific question; if cancer cells inexorably acquire more mutations over time, how did this cancer cell survive genetically intact for a millennium?

Robin’s scientific research career was recognised by many prizes, honorary degrees, awards and fellowships, notably of the Royal Society, the Academy of Medical Sciences, the European Molecular Biology Organization and the US Academy of Science. His honorary fellowship of the Royal College of Physicians recognised also his contributions to medicine.

In 1964 Robin married Margaret D’Costa, a teacher originally from Singapore. Their house in Finchley warmly welcomed visiting scientists, many of whom left with a jar of Robin’s jam, often a product of his lifelong passion for foraging. In retirement he immersed himself in music and history; he was particularly delighted to find that his paternal grandfather had been taught physics by Gregor Mendel in Brno, in what is now the Czech Republic.

He is survived by Margaret, and their daughters, Rachel and Helen, and grandchildren, Katriona, Jake and Shona.

Robin (Robert Anthony) Weiss, virologist, born 20 February 1940; died 27 February 2026