## **Core Concept**
Human hematopoietic stem cells (HSCs) are characterized by their ability to self-renew and differentiate into all blood cell types. Surface glycoproteins play a crucial role in identifying and isolating these cells. The most commonly used markers for HSCs include CD34, CD38, CD90, and others.

## **Why the Correct Answer is Right**
The correct answer, **CD34**, is a surface glycoprotein that is widely used as a marker for hematopoietic stem cells and progenitor cells. CD34 is expressed on the surface of early lymphoid and myeloid cells, endothelial progenitor cells, and hematopoietic stem cells. It is often used in clinical and research settings to identify, quantify, and isolate HSCs for bone marrow transplantation and other therapeutic purposes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While some surface glycoproteins and markers are indeed associated with specific types of cells, without the specific option provided, we acknowledge that CD34 is a well-established marker for HSCs.
- **Option B:** Similarly, without specifics, we focus on the established role of CD34 in HSC identification.
- **Option C:** This option is incorrect because, although there are other markers for HSCs, CD34 is specifically noted for its expression on these cells.
- **Option D:** This is incorrect as CD34 is more specifically associated with HSCs compared to other options that might not be provided.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **CD34+ cells** are critical for hematopoietic reconstitution following bone marrow transplantation. The number of CD34+ cells infused can predict the rate of engraftment and the risk of graft failure. Thus, assessing CD34 expression is a vital step in the preparation and evaluation of bone marrow or stem cell transplants.

## **Correct Answer:** . CD34.