Genomic Editor goes Personal

Decades long intense  research  of Jennifer Doudna and Emmanuelle Charpentier  culminated  in  Nobel Prize  in Chemistry in 2020.  The duo had hit upon a simple yet very accurate  way of editing the DNA chain  precisely at a given location.   Famous now as  CRISPR Cas-9 technology, this editing tool consists of an  RNA strip that guides  the razor sharp  bacterial enzyme Cas-9 to the exact location to do the correction work. Two books A crack in Creation and The Code Breaker  provide   detailed description  and analysis of this revolutionary technique.  

The medical implication of the discovery was  immediately obvious: that the DNA repair kit can search, find, delete/replace  faulty genes, thus making gene therapy a reality.   Indeed  FDA, USA  has  approved standard procedures  for a few  inherited diseases such as sickle cell anemia, thalassemia, cystic fibrosis, lukemia,  hemophilia, Huntington's disease  spinal muscular atrophy etc.  It takes years and money  to develop  genome editor kits, but  if pressed for time the whole process can be fast forwarded.    A recent issue of  New England Journal of Medicine  reports   how this tool was  customized to suit  a single recipient, racing against time.  

Baby KJ  now nearly 10 months old,  was born with a rare and serious  genetic  defect, termed  CPS1 deficiency.   CPS1, short for  Carbamoyl phosphate synthetase 1  is a key enzyme in the urea cycle  responsible for  converting ammonia into urea which  is then excreted through urine.  In  KJ's case both copies of  the CPS1 gene,  paternal and maternal  that he inherited  were found defective.    KJ was just 2 days old when this was diagnosed. As a temporary solution the baby  was immediately put on renal replacement therapy (RRT) to remove waste products, excess fluid, and electrolytes from the bloodstream.  Because for such patients the only curative option is  liver transplantation and   KJ was too young to undergo that.   The other option was to design  personalized gene therapy .  Normally this  would take years, but  KJ had no time to wait. 

Doctor  Rebecca Ahrens-Nicklas, is  a pediatric geneticist and Director of  Gene Therapy for Inherited Metabolic Disorders Program, at the Children's Hospital, Philadelphia and   Dr  Kiran Musunuru,  a cardiologist, geneticist and gene editor at Perelman School of Medicine, University of Penn. They with   their research teams  took up the challenge. The team  worked  at lightening speed. The first step was  analyzing  KJ's  genome to pinpoint  the exact nature and location of the defect.   This exercise   revealed   a  mutation at position 335 in the paternal copy and at position 714 in the maternal copy  of the CPS1 gene.  In both these positions   a stop codon  prematurely truncated   the formation of the  CPS1 enzyme.  The team decided to focus on the paternal copy. 

The  next step was to put together   a precise gene-editing tool.   A modified version of CRISPR, called base editing, which allowed the alteration of single DNA "letter" in the sequence was  chosen. Within 2 months  the repair kit nick named K-abe  loaded into lipid nanoparticles  was  ready  for trials.  First  the efficacy of K-abe was tested  in mouse and monkey models.  This was necessary to assess safe dosage  levels in terms of tolerance and toxicity.  In six months  the therapeutic kit was all set complete with all toxicological, safety and regulatory protocols.   KJ was slowly weaned off  the dialysis unit  and put on nitrogen scavenging medication and minimal protein diet.  

Doctors decided to start with   very low initial dose of K-abe , then later  hike up the dose  slowly and steadily.   KJ was 7 months old when he received  the first infusion.  Lipid nanoparticles carried the correction scheme to  KJ’s liver.  Dr Musunuru  sums it up  :  “CRISPR, a gene editor, enters the nucleus of the cell.  In this case, we programmed it to go to the site of the genetic variant that was causing the disease in KJ.”    As of  now KJ has had 3 infusions and he is doing very well. There is no ammonia build up in his system and his protein intake has been steadily  increased. He is growing up hale and healthy and his first birthday is fast approaching. 

KJ  with his tiny hands has pushed open the door to personalized gene therapy.   However  challenges remain:  such as  prohibitive  cost, complexity, safety etc.  and above all  ethical concerns abound.   

REFERENCES:

1. Patient-Specific In Vivo Gene Editing to Treat a Rare Genetic Disease    

2.  World's First Patient Treated with Personalized CRISPR Gene Editing Therapy at Children’s       Hospital of Philadelphia

3. World’s first personalized CRISPR therapy given to baby with genetic disease

                      

.