Cells in table automatically deleted

No, I am just writing a HTML code using the text editor.Here is a sample of the code that I wrote.
 
<div id=”anemiatable”>
<table>
<thead>
<tr>
<th>Adverse Event</th>
<th>Grade 1</th>
<th>Grade 2</th>
<th>Grade 3</th>
<th>Grade 4</th>
<th>Grade 5</th>
</tr>
</thead>
<tbody>
<tr>
<td>Left ventricular systolic dysfunction</td>
<td></td>
<td></td>
<td>Symptomatic due to drop in ejection fraction responsive to intervention</td>
<td>Refractory or poorly controlled heart failure due to drop in ejection fraction; intervention such as ventricular assist device, intravenous vasopressor support, or heart transplant indicated</td>
<td>Death</td>
</tr>
<tr>
<td colspan=”6″>Definition: A disorder characterized by failure of the left ventricle to produce adequate output despite an increase in distending pressure and in end-diastolic volume. Clinical manifestations may include dyspnea, orthopnea, and other signs and symptoms of pulmonary congestion and edema</td>
</tr>
<tr>
<td>Mitral valve disease</td>
<td>Asymptomatic valvular thickening with or without mild valvular regurgitation or stenosis by imaging</td>
<td>Asymptomatic; moderate regurgitation or stenosis by imaging</td>
<td>Symptomatic; severe regurgitation or stenosis by imaging; symptoms controlled with medical intervention</td>
<td>Life-threatening consequences; urgent intervention indicated (e.g., valve replacement, valvuloplasty)</td>
<td>Death</td>
</tr>
<tr>
<td colspan=”6″>Definition: A disorder characterized by a defect in mitral valve function or structure.</td>
</tr>
</tbody>
</table>
<div>