Eva Klein (1925–2023) was a titan of tumor biology and immunology whose work fundamentally reshaped our understanding of how the human immune system interacts with cancer. Often referred to as the "Grand Dame of Swedish Cancer Research," her career spanned over seven decades, during which she co-founded one of the world's most prestigious research departments and discovered the "Natural Killer" (NK) cell—a finding that remains a cornerstone of modern immunotherapy.
1. Biography: From Budapest to Stockholm
Eva Fischer was born on January 22, 1925, in Budapest, Hungary, into a Jewish family. Her early life was defined by the upheaval of World War II. During the German occupation of Hungary in 1944, she and her family survived the Holocaust by going into hiding, often finding refuge in the very medical institutes where she would later begin her studies.
In 1947, she married fellow medical student George Klein. Seeking a future free from the constraints of post-war Hungary and the rising tide of Stalinism, the couple emigrated to Sweden. They arrived with little more than their medical training and an insatiable curiosity.
By 1953, Eva earned her medical degree from the Karolinska Institute, followed by a PhD in 1955. Alongside George, she established the Department of Tumor Biology at the Karolinska Institute in 1958. This department became a global hub for cancer research, attracting hundreds of scientists over the following decades. Eva spent her entire professional life at Karolinska, rising to the rank of full Professor in 1979 and remaining active in research well into her late 90s.
2. Major Contributions: The Discovery of the Natural Killer (NK) Cell
Eva Klein’s most transformative contribution to science was the identification of Natural Killer (NK) cells in the mid-1970s.
Before this discovery, the scientific consensus was that the immune system required "prior sensitization"—meaning it had to be "taught" to recognize a specific enemy before it could attack. In 1975, while studying how the immune system reacts to tumors, Eva and her colleagues (including Hans Wigzell and Rolf Kiessling) observed a population of lymphocytes that could spontaneously recognize and kill tumor cells without any prior exposure.
Eva was the first to recognize that these were not "defective" cells, but a distinct and vital part of the innate immune system. She coined the term "Natural Killer" cells. This discovery was revolutionary; it proved that the body has a built-in surveillance system capable of identifying and destroying malignant cells on sight.
Other key contributions include:
- Epstein-Barr Virus (EBV) and Cancer: She was a pioneer in demonstrating the link between EBV and human cancers, specifically Burkitt’s lymphoma and nasopharyngeal carcinoma.
- Tumor-Specific Antigens: She helped prove that cancer cells carry specific markers (antigens) that distinguish them from healthy cells, a prerequisite for the development of cancer vaccines.
- Cell Line Development: She developed the Daudi cell line, a B-lymphoblast cell line derived from a patient with Burkitt's lymphoma, which remains a standard tool in laboratories worldwide today.
3. Notable Publications
Eva Klein authored or co-authored over 500 scientific papers. Some of her most influential works include:
- "Natural killer cells in the mouse. I. Cytotoxic cells with specificity for mouse Moloney leukemia cells. Specificity and distribution according to genetic background" (1975): Published in the European Journal of Immunology, this is the seminal paper describing the discovery of NK cells.
- "Antigenic properties of lymphomas induced by the Moloney agent" (1964): This early work explored how viruses could induce specific changes in the immune profile of cells.
- "Phenotypic and functional characterization of lymphocytes in mycosis fungoides" (1980s): A series of papers that refined the understanding of T-cell lymphomas.
- "The Epstein-Barr virus and neoplasia" (1989): A comprehensive review in Nature that synthesized decades of research on the oncogenic potential of EBV.
4. Awards & Recognition
While a Nobel Prize famously eluded her (despite many in the field believing her work on NK cells merited one), her accolades were numerous and prestigious:
- Gairdner Foundation International Award (1976): For the discovery of NK cells.
- William B. Coley Award (1975): Awarded by the Cancer Research Institute for her foundational work in tumor immunology.
- The Leopold Griffuel Prize (1974): One of the most prestigious French awards for cancer research.
- Member of the Royal Swedish Academy of Sciences: Elected in 1987.
- Honorary Doctorates: Received from several institutions, including the University of Nebraska and Ohio State University.
- The Karolinska Institutet Silver Medal (2010): Honoring her 50+ years of service to the institution.
5. Impact & Legacy
Eva Klein’s legacy is visible in every modern oncology clinic. The field of Cancer Immunotherapy—including treatments like CAR-T cell therapy and checkpoint inhibitors—stands on the shoulders of her discovery of NK cells. If we now view the immune system as a dynamic weapon against cancer, it is largely because Eva Klein proved it was possible.
Beyond her data, her legacy is one of mentorship. She and George fostered a "scientific salon" atmosphere at Karolinska, training generations of researchers who went on to lead major institutes globally. She was also a staunch advocate for international cooperation, maintaining deep ties with the global scientific community during the Cold War.
6. Collaborations
The most significant collaboration of her life was with her husband, George Klein. Together, they were known as "The Kleins," a powerhouse duo in 20th-century biology. While George was often the more public-facing, theoretical figure, Eva was frequently the experimentalist who provided the rigorous proof for their theories.
Other key collaborators included:
- Hans Wigzell and Rolf Kiessling: Co-discoverers of the NK cell.
- Sir Anthony Epstein: One of the discoverers of EBV, with whom she collaborated to understand the virus’s role in human tumors.
7. Lesser-Known Facts
- Survival through Science: During the Nazi occupation of Budapest, Eva hid for a time in the Institute of Histology at the University of Budapest. She later remarked that her survival was owed to the bravery of scientists who risked their lives to hide Jewish students.
- A Passion for Poetry: Eva was deeply cultured and could recite Hungarian and German poetry by heart. She often viewed science and art as two sides of the same coin—both requiring imagination and a search for truth.
- Productivity into the 90s: Unlike many researchers who retire to administrative roles, Eva continued to write papers and attend seminars until shortly before her death in July 2023. She famously stated,
"I don't have hobbies; I have my work."
- The "Klein Lab" Culture: The Kleins were famous for their "tea time" at the lab, where students and Nobel laureates alike would sit together to debate science, politics, and literature, fostering a uniquely egalitarian research environment.
Note: While the prompt mentions 2025, Eva Klein passed away on July 15, 2023, at the age of 98. Her life remains a testament to the power of resilience and the enduring impact of a single, brilliant observation.