I suppose it depends on what you mean by "now." For example:
Cellular enhancer for expressing genes in undifferentiated stem cells
US4959313A, granted 25Sep1990;
Methods and compositions for the optimization of human hematopoietic progenitor cell cultures
US5399493A, granted 21Mar1995;
Methods and compositions for isolation and growth of kidney tubule stem cells, in vitro kidney tubulogenesis and ex vivo construction of renal tubules
US5429938A, granted 4Jul1995.
So, again, I'm curious as to where you are reading Big Pharma can't patent their efforts within this aspect of medicine?
Pfizer's Stem Cell Research Policy: For more than a decade, Pfizer has been using animal or adult stem cells in its laboratories to help screen new compounds and identify safer and more effective medicines.
Merck: Together with the scientific community, we believe that research using stem cells has the potential to help identify medicines, therapies and vaccines that will treat, cure or prevent diseases and alleviate the suffering of patients with significant unmet medical needs...We have been conducting research into the biology of stem cells for more than a decade.
Roche: At Roche we are utilizing the enormous potential of human stem cells to test potential new drugs in vitro...At Roche, we are also investing effort in developing tri-dimensional culture systems for stem-cell derived stem cells, which would allow access to tissue models that are closer to an operating organ.
GSK:We have been involved in cell and gene therapy since 2010, working with Fondazione Telethon and the Ospedale San Raffaele, acting through their joint San Raffaele Telethon Institute for Gene Therapy (SR-TIGET), a world-leading research centre for stem cell gene therapy in Italy. SR-TIGET has been a pioneer in bringing gene therapy from preclinical studies to research in patients.
Do you think it's strange that they are throwing so much time, money, and personnel into an endeavor they feel can't be monetized?