Topic Discussion: CAR-T therapy and the Kidney

A new dawn is breaking in the field of hematologic malignancies, as the first product based on chimeric antigen receptor (CAR) T cells was scrutinized today by a panel of experts and unanimously recommended for approval at the FDA for pediatric and young adult patients (age 3-25 years) with relapsed or refractory acute lymphoblastic leukemia (ALL).

Blood is collected from the patient, and then autologous T cells are separated out and genetically engineered. The process involves inserting a CAR that targets CD19, an antigen expressed on B cells and tumors derived from B cells.  These CAR T cells are then infused back into the patient, who has undergone chemotherapy, and in the body the product homes in on B-cell leukemic cells and destroys them.  The main action happens mostly about 2 weeks after those CAR-T cells have been re-infused.  Some have termed this form of therapy as the “ living drug”

Autologous CAR-T cell therapy first shot into headlines about 4-5 years ago when it was thought about in CLL patients.   Then several other studies were done essentially confirming that the concept is correct but there are serious toxicities.

https://www.ncbi.nlm.nih.gov/pubmed/25317870 (leukemias)

https://www.ncbi.nlm.nih.gov/pubmed/26760100 (myelomas)

https://www.ncbi.nlm.nih.gov/pubmed/28029927 ( gliobastoma)

The technology is complicated and initially when tried in CLL led to multiple toxicities of various organs including CNS, cardiac, renal and mostly requiring ICU admissions from acute cytokine release syndrome. This happens due to high levels of IL-6, a cytokine that is secreted by T cells and macrophages in response to inflammation.  Etanercept and tocilizumab have been used to block the IL-6 activity to treat such side effects.

Acute renal injury following CAR T-cell infusion is multifactorial and almost always reversible. Reduced renal perfusion is often the most important cause of renal injury. Reduced renal perfusion can be caused by cytokine-mediated vasodilation, decreased cardiac output, or intravascular dehydration due to insensible losses from high fevers. Tumor lysis syndrome and drug effect from medications such as antibiotics are other possible causes of renal injury. Electrolyte disturbances, such as hyponatremia, hypokalemia, and hypophosphatemia are not uncommon but have been reported. A recent article in Blood summarizes all toxicities.

Now the therapy has returned and we may see this in many centers. We must be aware of the cytokine release storm that it can cause leading to AKI in that setting.  There might be more in the pipeline of similar products such as the one that just got approved for ALL.

Figure source: http://www.lymphomation.org/programing-t-cells.htm

Consult Rounds: Cholemic nephrosis or Bile cast nephrpathy or should we say Jaundice associated nephropathy

Bile cast nephropathy or also called cholemic nephrosis represents a spectrum of renal injury from proximal tubulopathy to intrarenal bile cast formation found in patients with severe liver dysfunction. Bile can be toxic directly to the tubule or can form casts and have similar damage as myeloma cast nephropathy.

Recently this entity has gained some interest in the literature.

1.      Classically seen with patients with acute or chronic liver disease

2.      Usually, the total bilirubins are over 20 and conjugated over 16 is the cases that had bilirubin casts on kidney biopsies

3.      The LFTS were also higher in these patients

4.      The cause of liver disease doesn’t matter

The mechanisms responsible for tubular dysfunction include uncoupling of mitochondrial phosphorylation (thereby decreasing ATPase activity) by bilirubin  and oxidative damage of tubular cell membranes as well as inhibition of Na-H and Na-K pumps in the tubular cell membranes by bile acids. Cholemic nephrosis is reversible provided bilirubin levels are reduced early. This recovery is however delayed if there is extensive bile cast formation.

Some have suggested jaundice-related nephropathy as a replacement for cholemic nephrosis. Based on their definition, jaundice-related nephropathy would encompass the spectrum of injury that ranges from proximal tubulopathy to extensive tubular injury and tubular pigment. 

As bile passes via tubules, there is pigment nephropathy.

Pathology findings include: extensive acute tubular injury with bile stained tubular casts.
Macroscopic findings will include bile stained yellowish discoloration of the kidneys in jaundiced patients which become dark green after formalin fixation.
The Hall's stain confirms bilirubin presence.

Other interesting articles on this topic

http://www.kidney-international.org/article/S0085-2538(15)56212-1/fulltext

http://onlinelibrary.wiley.com/doi/10.1111/hdi.12169/pdf

http://www.ajkd.org/article/S0272-6386(16)30488-7/abstract

https://www.karger.com/Article/Pdf/371689

Consult Rounds: Acyclovir and dialysis

An often unforgotten drug that we must be aware of in ESRD patients is acyclovir.

Acyclovir can accumulate in ESRD if not dosed appropriately and can lead to neurotoxicities- leading to confusion, tremors and coma.

Initial study of 7 patients with end stage kidney disease receiving hemodialysis looked at levels following hemodialysis with each patient received a single 800-mg tablet of acyclovir. Plasma acyclovir levels were monitored over the next 48 h as well as before and after the next routine dialysis. Peak plasma levels were achieved at 3 h (12.54 +/- 1.76 microM, range 8.5-17.5 microM) with the half-life calculated to be 20.2 +/- 4.6 h. Mean plasma level of 6.29 +/- 0.94 microM were within the quoted range to inhibit herpes zoster virus (4-8 microM) at 18 h. Hemodialysis (4-5 h) eliminated 51 +/- 11.5% of the acyclovir which remained at 48 h. Computer modelling of various dose modifications suggests that a loading dose of 400 mg and a maintenance dose of 200 mg twice daily is sufficient to maintain a mean plasma acyclovir level of 6.4 +/- 0.8 microM. A further loading dose (400 mg) after dialysis would raise the residual acyclovir concentration by 6.1 +/- 1.0 microM.

Acute acyclovir neurotoxicity can be treated in CKD and ESRD patients with dialysis. The drug is water soluble, not albumin bound and small- hence an ideal dialysis candidate for removal.  It is important to keep this toxicity in mind as many might come in to your office with non renal dosing of this agent on ESRD and CKD patients and can lead to neurotoxicity. PD is not an option; HD is preferred mode for removal of acyclovir. 

  Some references

http://www.ajkd.org/article/S0272-6386(12)70234-2/abstract

http://onlinelibrary.wiley.com/doi/10.1111/1346-8138.13196/pdf

http://www.revistanefrologia.com/en-publicacion-nefrologia-articulo-acyclovir-valacyclovir-neurotoxicity-in-patients-with-renal-failure-X2013251412000456

http://www.shmabstracts.com/abstract/the-monster-in-my-room-acyclovir-neurotoxicity-in-a-hemodialysis-patient